Raised ghuls and wraiths do not decompose to destruction when out of LOS
Undead raised with the necromancer's level 18 and 32 class power never crumple to dust outside LOS.
Problem
Corpses raised as ghuls or wraiths with the necromancer's level 18 and 32 class powers, respectively, will never fully decompose and crumple to dust outside of the PC's field of vision - their HP goes below zero, into the negatives. In a worst-case scenario this leads to things like:
"This is your loyal slave, a wraith (L: 1, DV: 20, PV: 0, Hits: -795(-795), A: 1, D: 3-13). [M]ore."
At that point, a single hit is enough to destroy them. But until that happens, you will keep on receiving messages about them decomposing a bit more, further decreasing their HP.
According sorear's wiki, this bug "happens possibly because the hitpoints are only checked with monsters in sight."
How to reproduce it
Use the class power to raise some undead, in a locked room where no monsters could attack them. Teleport away and wait a few hundred turns. Teleport back and 'l'ook at your slaves.
Notes
See above.