Huh. I'm could be wrong but all potions work off spell effects. Usually what bypasses dead magic is anything not written into the script, i.e. all spells not tagged in that code. This is often the case with modified spells with different labels, and seeing as how Layonara has modified so many aspects, it would not be surprising that maybe an overlooked potion spell that is customized is not tagged... perhaps even on purpose since healing potions would not really be threatening to the balance aspect as they aren't exactly a breeze to come by.
As for monsters casting spells, that's just how wild/ dead magic works. It only recognizes a PC. I've always rationalized this as the dominant power in the area has probably allowed it's minions to channel magic from it's own source.
That said... I'm not scripter. You'd have to ask one of the ten pound brains around here.
