peokai:

I don't use Tk, Glade, Gtk, et. al., so this is just a wild guess. You've probably already considered this, but just on the chance that you didn't: Are you using a proportional font in our text window? A proportional font causes just the symptom you're describing because each letter may have a different width on the screen. Using a monospaced font (Courier, for instance) would fix the problem if that's the case.

...roboticus