bug : corpse dust (level 7)

How to reproduce
1) the warrior talks to the old wand maker, if he tells you to get corpse dust
2) kill the old wand maker (with fire)
3) go get the corpse dust
=> the ghosts will follow you on this level and all the next levels until they kill you.

expected behavior = the ghosts will only follow you on this level but not the next ones.