Same issue here, and I agree that this makes gitk just about unusable. The issue seems to affect testing but not stable distribution.
Things I tried with no effect: - gitk 2.0 from git source repo - compiling latest stable tcl/tk 8.5 and 8.6 from their websites A fresh stable install works properly. apt-get upgrading and dist-upgrading to testing breaks gitk. However, I then reverted to the stable install and upgraded packages one or a few at a time and was able to upgrade all of them to testing with gitk rendering correctly at the end of the process. It seems that some dependency of gitk/tk/tcl breaks gitk between stable and testing but this breakage is dependent on the order of package upgrades. When gitk breaks it does so without X server restart, suggesting a client side issue.
