I'm not certain it's limited to Windows 8.1. The link in my previous reply said they found their ClearType contrast setting value was "gibberish" and when they changed it to a valid value (probably just by moving the slider in the ClearType Tuner program) the problem was resolved. I suspect if that value was corrupted the same problem would happen regardless of OS version. The question is how did that value get corrupted? I have no idea, and that could be an OS version-specific thing.
@David-san if you do want to turn ClearType back on you could give that a try. I don't think the conclusion is that ClearType and Arduino are incompatible but turning it off seemed to be the best initial troubleshooting step to me. Now that you've narrowed down the cause to ClearType it's easier to proceed to finding the exact cause of the problem if you're so inclined.