I may have found a bug. When I enter House Doemenel,

I tell the doorman I have a letter which may be of interest. The letter is in my quest items. I can go to Abrecan and give him the letter right away, in which case he gets angry about me killing his lackeys (why my character would admit to it is beyond me). However, if I chat with him first about the animancy hearings and then suggest it's in his best interests to work together, he tells me his lackeys used his letterhead, and that he would like me to retrieve the evidence. I agree, but I can't give him the letter in my possession. It just goes to the "Where can I find these thieves?" dialogue. If I close that, I can't even talk to him again. If I exit the house and re-enter, he says, "Have you procured the letter?" but I still can't give it to him. I can only say that I'm still looking for it (in my voluminous pockets I suppose). I don't know if it makes any difference, but I already have the diamond as well, having taken the opportunity to procure it when I first entered the district - who can resist an unlocked window? It's not a huge deal, as I can just give him the letter when I first arrive, but it might spare other players a reload and a few wine stains.

 

I also have this bug, and it's a bit of a pain since my prior saves are way back before I turned down the first opportunity to give Abrecan the letter. I tried advancing the quest manually using a console command, but his dialogue is stuck in the same phase regardless of the state of the quest log.