There are two bugs currently occurring in Flock 2.5.2 in regards to Flickr logging out:
Bug 17221: At some point within 24 hours (sometimes many hours, sometimes only a few), Flickr logs out.
Bug 17021: Flickr logs out when you restart the browser.
These issues have been fixed in Flock 2.5.6, which is now available from flock.com. Auto-updates are not available at this time, so you will have to manually upgrade. Instructions are available at http://getsatisfaction.com/flock/topics/flock_2_5_6_now_available_fixes_flickr_and_twitter_issues
