This happens for me at least with a contact on MSN and ICQ. MSN is the first listed icon, ICQ is the second. He is not logged into MSN but he is logged into ICQ. It shows both as offline. Ironically it still lets me communicate with him via ICQ even though it insists that he is not online.
It has something to do with the serverside list wish is not updated or something like that. I'm sure this is a duplicate bug, but i'll let Stphan close it :-)
This is not the bug you assume it is, but rather yet another duplicate of Bug #61223. *** This bug has been marked as a duplicate of 61223 ***