This is a really annoying bug. Offline psybnc-user sometimes changing this nickname to GuestNNNNN and original nick peroidically when it has not configured guest protection on NickServ (after netsplit for example), and it looks like:
* blablabla has changed nick to: Guest41565
* Guest4155 has changed nick to: blablabla
* blablabla has changed nick to: Guest3556
* Guest3556 has changed nick to: blablabla
And it changes nick again and again, channel mode +N (no nickname changing) helps, but it's not problem solvation! Please, try to fix that
