Those three quests are unfortunately known to be broken under various circumstances. I'm working on a quest system rewrite at the moment, which should hopefully solve the bugs people have been reporting.
Leprosy must have some kind of exception happening on every turn refresh. I'll take a look, though I think I know the culprit.
999 damage? Definitely not intended. I thought I scaled back explosive damage in the last update. Hm. I'll take another look at that code.