Comment 3 for bug 120858

Probably, it's at least an interaction between gnome-terminal and your X driver; where the bug lies is hard to say. I'm adding xserver-xorg-video-ati so that between the two, perhaps we can find the bug in one or both. Perhaps its a duplicate of bug 34435, though AFAICT the symptoms are different from that bug and its duplicates. However, it mentions problems with the XRENDER extension, used via Cairo in most apps, which gnome-terminal also uses.

Are you able to reproduce this problem in xfce4-terminal (which shares the same library code for the terminal emulation widget as gnome-terminal)?