Another undead bug?

[Deadman]

I know that wind up/pump style attacks prevent the undead passive from working, but i was just victim to another buggy behaviour i think, as my ghostly skull died to his reflected ghostly bite and didn't return. Anyone else noticed behaviour like this?

[Gendou]

There's a known bug with undead and mechanical resurrections.
As you mentioned, two-round abilities seem to disable it.
But sometimes other abilities seem to do the same thing (abilities with built-in stuns, for example).

It's a known bug, and it's on the patch notes for 5.2 to be fixed.