Nope, I'm pretty sure that is part of the board engine design that the images are directly related to avatars.
It was a bug, I did mean to fix it but I chose not to for a couple of reasons. Primarily I couldn't be bothered, but also I figured that anyone who wasn't particularly bothered about an avatar wouldn't be bothered about their "rank" being displayed either. Plus I thought it might encourage people to use avatars.