ZDoom

It appears that the morphing subsystem completely ignores the ACS SetActorProperty for APROP_SpawnHealth, so if you set a class's health to something above the norm, then morph and revert, it sets your health to the original class's spawn health, NOT the health set by ACS.

APROP_SpawnHealth is a misnomer. It actually sets the player's MaxHealth, not their SpawnHealth. (I do not know why it has the wrong name.) Under normal circumstances, setting the spawn health is useless, since it only affects newly spawned actors. As such, there isn't even a SpawnHealth property. The spawn health is simply the default value for Health and thus shared by all instances of the class.

An UnmorphHealth property might be useful, but that's entering the realm of feature suggestion.