OK, couldn't find anything on this in a search, but correct me if I'm wrong
Anyway, as shown in the pic, the Tab name is different from their actual name - the name in the tab is actually the name the person had last night, and after closing and re-opening it is still the same.
Using Latest MSN Messenger + Latest MsgPlus + Stuffplug Beta (latest) on Win XP SP1.
Happened after a clean startup.