When I disturb the graves, kill undead emerging out of them, go to other level map and then go back, 2 of 6 graves are earthed back and refilled with new undead.
To check the issue you can use my savegame uploaded here:
http://dfiles.ru/files/b2q3a5bsr (~11 Mb)
Disturb 2 of 6 graves on that map, go to Lake Nur level, than go back and see the graves refilled with new dwellers... and loot
