This is on the current cao build (5.2?)
If my flaming corpse servant kills something by setting it on fire, it does not seem to count as an undead-servant kill for Y piety purposes (no "accepts your undead slave's kill" message), although it does count as a collateral kill for all other purposes.
Cyrus
I know what's going on here - monster enchantments don't track the monster that afflicted them, only whether that monster was allied. So Y never knew that the sticky flame was undead's fault. Not sure what the best fix here; recording monster links is very awkward to get right in the face of monsters moving across levels, dying, etc.