I have been experiencing this bug too.
My soc mates asked me why I had been loging in and out at strange hours (3-4 am) without saying anything, not even "hi", they thought I was being rude
Of course, I had not loged in at those hours, so I was scared (although I own a GC too), and filed a support case. The support guys were very friendly and did some searches on their database, and told me that all logins with my account came from the same computer (different IPs, since they are dynamic, but same
EU client), and that I had never loged in at those hours (all logins came from 4pm to 11pm, aprox).
So, I was quite confident this is a bug, where for some reason, avatars are incorrectly shown in chat as logging in or out.
/jdegre.