In short Pidgin thinks AIM and ICQ are one in the same,
but for me ONLY uses the ICQ buddy list.
Pidgin will not load ICQ or AIM correctly.
It loads them both as ICQ and does not include the AIM buddy list.
Which is a different buddy list.
Same user name.
GAIM used server login.oscar.aol.com , but not anymore.
But in gaim in order to load ICQ you have to use your ICQ Number,
not username, and pidgin seems to work opposite.
ALTHOUGH If I recall correctly, they are both using the same address
to connect with, but GAIM used OSCAR for ICQ.
So that is a few things that are weird.
Try running the same from a local install of pidgin. If it still does it there, this would be an issue with Pidgin and you'll have to take it up with the guys over there.