Jaimie Still like this in 0.78.4 btw.
This is a local issue on your mac, but I have no idea what caused it and how you can fix it.
First I thought it was related to BS, but Usenapp on my macbook running BS beta 2 works fine.
Does the threads pane looks the same for a new created subscription?
Maybe the preferences file got corrupted while upgrading.
You can try to reset it with the following command (close Usenapp first)
/usr/bin/defaults delete /Users/[username]/Library/Preferences/com.xoroxsoft.usenapp.plist
and do a reboot.
Or doing above and also remove the whole usenapp database and configuration files by deleting
/Users/[username]/Library/Application Support/Usenapp
(make a backup first)
Anyway, it's not an easy one.