I haven't noticed GAIM acting funny on file transfers as I've
never tried it for that purpose.

You may want to look into the recent answer
to GAIM's bugs, called "Pidgin". It's basically
the same program, with a new name,
and it's not in beta, but at 2.0.1.

From the website: "We've released version 2.0.1 of Pidgin
(formerly Gaim). This is a bugfix release addressing over 100
bugs reported in 2.0.0. Keep those bugs coming in, and we'll
continue making regular, frequent releases."
http://www.pidgin.im/

I use it in Fiesty Fawn Xubuntu (and Windows XP) and it works
great, again I haven't tried transferring files with it, but you
may want to give it a shot and see if it helps you out.