@Amarathiel Thanks, it seems that only my bd is cursed then :D
1) Gonna make a video about it, it doesn't seem to be a common problem
2) The Dark Bargain buff lasts 6 seconds after the thrall disappears, doesn't it? Even if I stand still in F12, summon the thrall, get some marks, then let it expire / distmiss it, it seems to be "random" for me when I can use the Funeral Pyre :(