yeah i have this problem as well, just then i signed into my msn and opened up firefox and it went over all my contacts :/,
i then unticked "always on top" and reticked it for every single floating contact and htey are now all back on top
![:S](images/smilies/msn_confused.gif)
this is extremely annoying tho
![:P](images/smilies/msn_tongue.gif)
i hope u find the bug and fix it soon patchou!