Corpses disappearing from empire-style crypt
1) Start a game on Hell's Deep. Select the "Arcane" theme (I believe the "Empire" theme should work too).
2) Build a Crypt. I used 3*5 for my testing.
3) Grab three empire units from the toybox. Drop two onto one crypt pyre and one onto the other.
4) Wait until you attract a Necromancer, who should go to the Crypt to start raising ghouls. Keep the cursor hovered over the crypt so you can see the corpse count.
It's tough for me to work out exactly what's going on here. It looks like the corpse count goes down while the necromancer is trying to get into position to raise ghouls, without a ghoul actually appearing. When I test this with about three corpses in the crypt, the necromancer is generally able to get one ghoul out of it.
I'm pretty confident that the standard Underlord-style crypt is fine.