If getting punched dispels, punching does too. When I see your Eye of the Cat, I punch you and it's cancelled.
Oh sorry, I meant I place my finger in your hand's path so you're the one hitting me. :mrgreen:
Because of that, the spell can only be suppressed while MR is touching you and reverts to active afterward. Yes, it is a catch-22.
Interesting question.
I tend to think that no: With regular MR, when you punch someone, your MR doesn't enter play, even if it is a corpse animated by Rego magics.
This works exactly the same way, save that, when a minor spell doesn't penetrate, it is instead canceled.
Yet, even if it is:
I don't understand what you mean by your "finger in your hand's path" phrase.
The base principle works too with supress, but I'm not sure there wouldn't be more problems, and I don't like the picture of, say a staff growing throrns, the thorns disappearing when he strikes a faerie, coming back as he swings back, disappearing again, and so forth.
Same with a low-level MuCo spell: when striking someone, your appearance would falter with each strike 
The approach to Parma I use is to say that when something with magical qualities bounces off parma, you take the lesser of the magical effect and the mundane equivalent.
So if a pink-dotted sword hits, the magical colour is pink and the mundane one is non-existent. So the magical pinkness has no effect. The weight, hardnesss and sharpness of the sword are not affected by the magic, so you still get wounded.
If you magically sharpen the sword, then the magical sharpness is reduced to the mundane amount you already had, so there is no practical effect. If you magically blunt the sword, then it acts as a blunt sword - the mundane sharpness has been suppressed by the spell.
If you turn water into poison, the parma makes the liquid only as poisonous as the mundane water. If you turn poison into water, then the spell suppresses the poison so the drinker is fine.
If you throw an entirely magical rock at a mage, there's no mundane hardness or weight so there's no effect on him. If you rego a real rock, then the speed at which it moves is magical so doesn't hurt him. If you make a boulder into a pebble, then he gets hurt by the pebble, just as he would if you made a pebble into a boulder.
The trick comes when the mage acts on something magical, like a magic bridge. But here we have action going the other way, and I say that parma doesn't kick in on the mage's actions. So his stepping on a bridge is unaffected by parma, although the bridge falling on him would be. If he falls on the bridge, then he probably gets hurt. If he and the bridge leap at one another from opposite cliffs, then the player deserves whatever you feel like doing to him 
Hmm... the poison/water thing does not seem to fly. It is intelligent magic resistance. Nothing wrong by it "per se", but some people have qualms about it.
Water to poison --> poison supressed --> water --> no damage
Poison to water --> water NOT supressed --> no damage
????
It does not read very logical to me....
Xavi
Black Sabbath - War Pigs
I think people go too far in trying to close all the holes in parma as a defense. It's better to limit it to stopping effects that directly target the magus, conjured stuff, conjured forces and transformed stuff* than to have it so broad that looking at the consequences logically makes the game unplayable without bizarre contortions and exceptions or an unwritten rule that a thousand curious wizards just don't go there when it comes to investigating a core part of their power. And a parma thus limited is still a damn good defense that will stop most non-hermetic magic attacks and even most of the hermetic attack spells that aren't specifically designed as mage killers. Yes, a narrower interpretation of parma makes it easier for characters to find a way around it but you know what - magi are clever and powerful folks and however good you make the parma magica they will find a way to kill someone if the really want to. What makes the parma so valuable is that it stops them having to want to.
The parma is the OoH's most prized secret because it allows magi to socialise, to build up trusting relationships, to teach, to share their secrets. The magic of the order is so strong because hundreds of magi have collaborated over 400 years to improve it. If you are seeking rules that devalue the parma look not for holes in the defense it provides but for other widespread ways of getting around the social problems posed by the gift. I haven't read Rival Orders but I hope that they consist of a few dozen people who may be individually powerful but find it really hard to tolerate each other and pass on their power or have a damn good, interesting reason why not.
*which does after all cover all the description and examples of MR in the core book.
Physics gives the same results no matter the referential system: hitting and being hit is the same thing.
This isn't true in Mythic Europe: hitting a magic wall does you damage while being hit doesn't. Therefore when you punch, you are the one acting and only your Eye of the Cat is dispelled. If both are punching, both are acting and both lose their Eye of the Cat. Even if you do your best not to hit me, as long as you are moving a body part I can put myself in your path. You will be the one who hits me because my finger got there before your elbow, and boom your spells got dispelled.
Water is a basic liquid, it has nothing special about it. It's an element, in fact.
Poison, on the other hand, is a liquid with extra qualities.
If you add those qualities magically by turning water into poison, they can't act through the parma becase they're magical and the parma suppresses magical stuff. If you turn poison into water, you don't add any qualities, you just take some away. So there's nothing there to do any damage, and nothing for the parma to act on.
My bold, and in answer to the bolded bit, if you just take the poisonousness away that's Pe and the poison does not come back at the end of the spell. Muto reversibly changes/suppresses the poison so the liquid in the goblet is magical. That is enough to to get it past an InAq poison detector (but not an InVi something's up detector) and, if you have "intelligent parma" that stops harm rather than magic, past that too. Then at sunset the wizard gets an acute case of poisoning.
The important thing to remember, whatever interpretation or house rule you are using, is it it OK for the wizard to get poisoned. Perfect defenses are dull, if the only thing you can do against your enemies (or they against you) is build up an enormous penetration or use a RAW rock lobber and anything clever you try gets shot down then that's a saga to walk from.
Oh agreed, but although mutating a poison into water isn't just taking the poison away, that is one of the effects. You may also change the colour, and the consistency, and the taste and smell, all of which are almost certainly muto rather than perdo. Perhaps I was clumsy in talking about "taking it away": what I mean is that the muto spell has changed the level of poison in the liquid, and in my view parma limits its impact to the lower level. So if you were to muto a strong poison to a mild one, you'd get hurt by the poison in its changed potency* - viz, not as much, but still slightly.
Of course this starts heading towards the debate about the precise distinction between muto on the one hand and perdo/creo on the other, which is a whole other can of worms.
I'd probably also say that the liquid ceases to be a liquid once imbibed, and once it's incorporated in the body it's gone. If you drink poison it has an immediate effect, changing the healthy body to an ill one; so if the erstwhile poison you drank in aqueous form has no effect on you, then when the spell duration expires there's nothing left to turn back into poison. A live man turned into a frog for a diameter and squashed during that time doesn't turn back into a live man.
*assuming you treat toxicity as a single quality which can exist in a range of degrees - say, adder venom is 3 or 4 times as poisonous as a bee sting. I'm probably happy to do that, as it fits with the classical/mediaeval desire to categorise things into similar types, but I can see an alternative argument that you've eliminated the adder venom so it can't hurt you because it's not there, but the bee sting is magical and so also can't hurt you as the parma suppresses it. Perhaps the sharp/very sharp/blunt sword would be a clearer example.
I don't think so. Consider if you will a spell to turn dirt into nourishing soup duration diameter. Under your interpretation a mage can sustain herself indefinitely with this spell without vis and never end up with a stomach or veins full of dirt.
Well no - the parma would suppress the magically-created properties, so the dirt turned into food would be no more nourishing than the dirt.
In any case, RAW states that magically-created food doesn't nourish, so that's perhaps a bad example. You can't magically add nourishment without vis.