I've noticed that if I just have Usenapp open and in a newsgroup that after a while of not being used (not actively downloading anything) it will seemingly close out of the newsgroup (no messages shown in the right pane). I have to click on the newsgroup again to bring up all of the messages and find my place again.
Has this been happening for a while or just once after you upgrade Usenapp?
It happens pretty consistently. One time I saw it happen when I plugged my laptop in to its external monitor. I don't know if that's a coincidence.
It just did it after I closed the lid on my laptop at home and then opened it once I got to work.
It is better to close Usenapp before putting your MacBook to sleep. Not that it's mandatory, but there may be no network available when you start using the MacBook again. This will recover after some time, but it may take a while.