Windows 7 x64 - Radeon 7850 here, been having this exact same issue since the game was released, sometimes the font is great and then after some minutes or after I enter\exit combat this happen. I really wish they would had fixed by now. My monitor resolution is 1600x900, from what I understand its not a very common one, still, had no issues with it.
Pastebin for debug.err (made it to expire in a month): http://pastebin.com/8Nz2U2f3
Edit: Forgot to say, I do not use MSI afterburner.
Another edit: More info, and another thing that may be useful mentioning, on the Video settings in control panel, theres a tab where I can set the text to 100, 125 and 150%, and mine is set to 125%.
I set it back to 100% (default) to test, problem still persists. Saw something that I havent noticed before: in the build menu, when I alternated the mouse hovering in the tooltips, one was fine while the other was "garbled".
Picture: Font 1 and Font 2