Avatar display on article pages

There seems to be a problem in the way avatars are shown in the Top Rated Comments of a news article.

Users without avatars have the plain grey head shown, and this works fine. But for users with avatars, their image is only placed over the top of the grey head, rather than replacing it. Consequently users who have transparent sections in their avatars (arn would be a prominent example) still have the grey head shown underneath their avatar.

Wasn't sure if admins were aware of this issue/bug.

(attached images taken from this article)