Vlad,
I don't know if this has been brought up before, however, if you go to the Vale of Shadows cave after speaking with Lysan in the tavern, but before accepting the quest from Kresselack, Lysan is there retreating, and tells you to buzz off basically, but after you say "OK" she is perfectly happy to sit there stupidly looking on while you loot her locked boxes. It just strikes me that this may be something that would cause her to go hostile. Not sure if that is something that can be fixed easily or not.
Ant