You bring a fair point which I'll take some time to consider.
You misunderstand me completely - which happens. But I believe to have explained myself here already sufficiently.
Hi,
I suppose I'll give it a go.
Let's start off with what these targets are. A target of individual or group is of the form of the spell. To Target a group of minds I use mendham. A group of sheep? Animal. But targets such as room, structure or boundary r containers. These are arbitrary constructs that have nothing to do with the form being affected.
The other thing that I think I remember correctly is that a spell takes effect immediately and lasts for its duration rather than continually applying itself over its duration. So if I mind control everyone in a room for a month, the people being mind controlled stay mind controlled even when they leave the room to execute my nefarious demands, and people who newly enter the room are not themselves mind controlled. New paragraph
In a similar way, if I have a ship, and cast a spell that affects everything on the ship, everything is affected even when it leaves the ship, but anything that boards the ship is not affected by that spell. Also, the ship moving or being destroyed has no effect on this. The spell used the ship as a container to satisfy the target specified, but the magic itself affects the forms at spell casting time. New paragraph
It is possible to create weird spells that behave differently, such as treading the Ashen path, but these are exceptions that must be specifically designed to act in this way and require permission to work because it is not always apt. And, of course, the spell gets an extra magnitude or two for being special.
But let us go back to normal spells.
If I have a spell on a ship that kills the rats, I need to reapply it to kill any new rats. If I have a spell on a ship that controls magic, I need to keep applying it to control magic, unless we have some idea or concept of their being a magical heck I'll call it a field that is being controlled, in which case that field is controlled for the duration. This is a modern sounding term, but it seems closest to what an aegis is doing. Otherwise, totally leaving aside movement, how can it affect any new magic introduced to the area? After all, there is no form for area, certainly not them. Or, we can say that in aegis is similar to treading the Ashen path, and that is what makes it special. And then we do not need the field or some concept like it because the spell continually and repeatedly affects its form as usual. New paragraph
I think that this ambiguity will help us solve the problem. If the spell had an immediate effect that changes the local magical field, moving the boundary will do nothing, nor will eradicating it. The spell has already had its effect, which will last for a year, similar to the way a mind control spell that affect the boundary does its thing one time and then persists upon the affected Target. New paragraph
But if the spell is like treading the Ash and path, and is therefore weird, then moving the boundary will will affect the new region. And this would then leave us with a question of what happens to the previous region. If it is exactly like treading the Ashen path, which applies a momentary effect repeatedly over the duration of the spell, the previous region affected by the aegis is no longer affected. But if the aegis not only applies itself repeatedly for the spell duration, but each application persists for the spell duration, then you get this ever growing aegis as the region affected by the spell changes. Either way, destroying the boundary would stop any future applications of the aegis, because the boundary defined by the spell is gone. This means that the momentary version applied repeatedly for a year would stop as soon as the boundary is no longer a valid boundary.
So, I think there are three valid interpretations for what happens to in aegis. The most simple and straightforward is that when the boundary moves nothing changes and the region previously affected remains affected and no new region is affected. Destroying the boundary similarly has no effect. But the rules support other interpretations that would apply specifically to spells that are designed that way. The aegis is a very special spell and perhaps is designed that way. New paragraph
What about haunt of the living ghost? My answer is it's a mystery virtue, it looks like a spell but it's weird and different and not completely hermetic anyway. So it can do what it wants. But we can say, if we want, that it works like treading the Ash and path, continually maintaining the ghost as though it will recast every moment. New paragraph
This might be wrong in all sorts of ways, because I don't remember my books and I certainly am not about to open one because that would hurt. But that's what it looks like to me.
And now I get to collect some experience points in magic theory 
Anyway,
Ken
As I mentioned once elsewhere n this topic- if your boundary target can move, what happens when your flying castle with an aegis flies over a magical tree with might:10? Does the castles aegis cause the castle to bounce off? Does it uproot the tree? This is not a simple or trivial change we are talking about.
No. That's one "type" of "place Target" (I call it type 3, above). Like Incantation of the Putrid Wine, that makes all liquids in the room at the time of casting vile, and they stay vile even if brought out of the room, while no new liquid brought into the room later becomes affected.
But another "type" exists (I call it type 2, above). It affects all things that happen to be in the place during the entire effect's duration, while they stay in the place. The Shrouded Glen: anyone in the target forest gets lost, for the duration of the spell (yes, this is mind control, constantly renewed on new folks). Well Without Light: all light within the target structure is smothered for the duration, including new light you bring into it. Aegis of the Hearth: opposes foreign supernatural powers brought into the target Boundary for the duration - those that can get out are no longer opposed.
I'd say this is more common in folklore and myths, and also less prone to the type of abuse where you create a temporary "place" (e.g. a room) via magic for the briefest duration, so that you can then target everyone within it with a long-lasting effect ... and then you just "erase" the room but what you have ensorcelled stays ensorcelled.
Assuming that the aegis extends all the way down to the tree, the aegis enfolds the tree - that suffers an appropriate reduction of its magical puissance until the aegis moves away.
Note that a mobile aegis enfolding an immobile tree is different from a mobile tree (attempting) moving into an immobile aegis! Remember that many of the "symmetries" of newtonian physics do not apply to ArM5 cosmology: if a magus turns into a giant through a low penetration spell, and then tries to punch a real giant of sufficient Might, his punch is stopped by the giant's MR... but if the giant then punches back the magus, the fist connects with full force!
And that simple rule is confirmed by LoH p.123 box.
Quite. TMRE p.73 The Haunt uses the Target parameter of p.71 Bind the Living Ghosts to define the Haunt. This goes beyond the standard Target parameters from ArM5 p.111ff Spell Design.
I think this has been resolved in the process of sorting out Ring/Circle, if taken with the sidebar in LoH.
Is there anything major outstanding?
It's still not 100% clear to me how it's been resolved It seems to me that what you are saying is the following:
A magus can define at the time a T:Boundary spell is invented how that spell works. In particular if:
a) the spell affects for its duration everything that was, at the time of casting, in the boundary, or that
b) the spell affects for its duration everything that is in the physical space that was occupied by the boundary at the time of casting.
The magus can however never choose that:
c) the spell affects for its duration everything that is in the boundary.
If that's really the case, one would have to at the very least
- explicitly state in the corebook, rather than (only) in a sidebar of a "highly non-core book".
- explain that in this, boundary acts differently from all other Container Targets, that work instead as either a) or c), and never b).
This is really important, because it's very easy to assume that if a T:Circle spell moves with the ... Circle, a T:Room spell cast on a boat moves with the boat, a T:Structure spell cast on a ship moves with a ship, then a T:Boundary spell cast on a ... ship! moves with the ship, rather than leaving behind a ghostly ship-shaped afterimage of magical energies as it does in b). - errata Haunt of the Living Ghost
- make sure that there is no published covenant (or suggestion of a covenant) with an aegis on a "Delos-like" moving island or on ship/ fleet of ships. This last is rather sad, I think, because it rules out many interesting saga possibilities based on the concept of Semita Errabunda, but with a covenant that moves "classically" rather than by warping space.
As mentioned above, I think this is really a sad choice (in that reduces fun game concepts, complicates the game, and introduces a mechanic (b) that definitelly is not "mythic"); and it would be much more effective to simply replace the LoH sidebar with one on "The mystery of the missing Aegis" offering tantalizing hints about why Tomae had none ... and ultimately leaving it as a mystery for players to solve.
But in all fairness e.g. One Shot sees it differently.
Or T:Boundary can only be cast on unmovable entities. By stating it explicitely in the target definition, readers will realize this constrain does not apply to T:Room.
Very few things are truly unmovable.
I don't think it's an issue for most AotH.
Are you thinking of the boundary of a forest when you cut up some trees?
Or are you thinking a forest* can move?
*using forest as a default entity, don't expect too much sense.
Well, imagine a covenant on a mountain peak. What if you use a rego terram.spell with enough size magnitude to move the mountain a few miles away?
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From tL&tL, p.20:
one Merinita magus even moved a hill two miles south!
[to make access to a vis source easier]
The move a mountain example is a fun case where we can have a conversation about whether its better to have a flying aegis, or whether enabling another magi moving your covenant outside of your warded boundary without needing to penetrate is better.
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OK, here is an expanded Container Targets insert. Comments?
Container Targets
Spells with "container" Targets, including Circle, Room, Structure, and Boundary, can work in one of two ways.
First, they can affect any valid target within the Target container at the time of casting, and continue to affect those targets even if they leave the original Target area, for as long as the spell lasts. It does not affect anything that enters the Target container later, even if the spell is still in effect.
Second, they can affect any valid target within the Target container during the spell's period of effect. In this case, a valid target that leaves the container ceases to be affected by the spell, and a valid target that enters (or re-enters) the container is affected, until it leaves or the spell expires.
The way that a particular spell works is fixed when it is designed, and cannot be changed by the casting magus, although a spell working in one way is similar to a spell that is identical apart from working in the other, and so knowledge of one gives a bonus to inventing the other.
For example, a spell to put pink dots on people's foreheads with Target: Room and Duration: Moon could work in two ways. In the version that works in the first way, everyone in the room (on whom the spell Penetrates) at the time of casting gets a pink dot on their forehead, and this pink dot remains on their forehead until the new moon and full moon have both set. In the version that works in the second way, anyone who is inside the room (on whom the spell Penetrates) until the new moon and full moon have both set gets a pink dot on their forehead, even if they were not in the room when the spell was cast. When they leave the room, the pink dot disappears, although it reappears if they go back into the room. These two versions are two different spells, and a maga who wants to cast both (and cannot reliably cast them spontaneously) needs to create two spells.
If the container ceases to exist as a container before the spell duration ends, the effect depends on the type of spell. If it is of the second type, the spell ends when the container ceases to exist. For example, removing the roof and one wall of a Room would mean that there was no longer a Room, as would placing a wall down the middle of the room. If it is of the first type, the spell is unaffected, unless the Target is Circle, in which case it ends when the circle is broken.
Most containers do not normally move, but they can. A Structure, for example, can be a ship. This is irrelevant to spells of the first type, which affect anything within the container at the time of casting, no matter what happens after that. Spells of the second type move with the container. Note that wards, including Aegis of the Hearth, are all of the first type, and target the interior of the container at the time of casting. If the container moves, part of it moves outside the ward. (Note also that, in Mythic Europe, the earth neither spins nor moves through space: things that do not move relative to the earth do not move at all.)
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Do you mean Ring instead of Circle?
I like the content!
Spells "of first type" and "of second type" are excellent for discussing it.
But perhaps this classification could be rephrased in the later rule? Perhaps classifying spell containers instead of spells: "spell of first type" => "container for casting duration" or briefly "casting container", and "spell of second type" => "container for effect duration" or briefly "effect container"?
So... you can't have wards on containers that move with them?
For example, you can't ward a ship against fire?
I just fail to understand the purpose behind this clause 
Other than this it seems a very fine resolution of the issue.
Anyway, it is currently valid also for T: Circle alone, independent of D: Ring.