I tried replicating the login problem today, and I couldn't, so maybe it got fixed along with the Classifieds, because the chain of events, as far as I can recall, was:

1, Log in via the login panel on the main site, checking "Remember me".
2, View Classifieds.
3, Go to Community -> Forums
4, Discover I was logged out.

Anyway, I had no problems whatsoever when I tried it again just now.