Dr Elrath is very strange, I may say.
First time I met him in Poor Area, where I was unable to talk with him (he leaved when cut-scene ended). Then we met again in his house, where I... hm... just looked - nothing more :)... at his chests :), he was displeased with such an action and banished me from his house and _leave_. It was before I have found his poison barrels, when I got a quest log update to meet him. And after that I never seen him (of course I picklocked his house and got familiarized with his belongings :).
And only when I leave his cellars with some of his stuff he arrived to try to blame me for this. But quest record stating "Meet with Dr Elrath" or something remain unresolved, yet whole quest became resolved.
Is it ok, or it is my... incorrect behavior... broke the plot?
