Thief quest does seem to be bugged from a climbing aspect though most people either don't realize they have to climb to get to him. Not once, but twice.
However, the "finding the valuables" quest is bugged to hell. First time I tried it, I only got 3 drops. Every time after, the villa is empty. Boooo!
I also don't think these are repeatable but I could be wrong. I've never been given the option to repeat after I went through the 2nd part of the quests.