Here's where the constant effect issue was discussed: https://forum.atlas-games.com/t/permanent-control-enchantment/10041/1.
As far as an example. Callen maga creates an object that is constant in effect, she gets into an argument with my magus, who is a counterspelling fiend and he dispells the effect. The item (or at least the invested effect) is now useless, since the effect cannot be recast at the next sunrise/sunset. The reasoning is that D:Sun, 2x/day environmental trigger is how one pays for constant effects, and it works by casting the effect once and being done. The effect cannot be recast on another recipient at a later time, and never expires, unless the item is broken (although I question this, somewhat), the effect is dispelled or the item is disenchanted. Of course, dispelling the effect is much easier, and doesn't even require the presence of the item to effectively destroy it.