I'm sporadically facing the login dialog when working in PW. (So I'm surely already logged in.)
If I log in a second time I can go on until I want to save. PW guesses to be cheated.
Loosing all the work done so far is really not amusing at all.
I suspect this happens (Firefox 14.0.1) if I copy and paste between tabs (and domains).
I have not investigated this issue a lot. I don't expect anybody else to do this for me. I'm just wondering, whether someone has the same experience and then maybe can give me a clue.