I recently experienced what could be misinterpreted as a bug in Visual Studio 2008. While feverishly typing code, the language "randomly" changed to Chinese. Here's what it looked like:
Of course it's not a a bug--it's a feature! Left ALT + SHIFT is the Windows shortcut for changing the input language, and since I use ALT and SHIFT so frequently in Visual Studio, I occasionally hit the keys at the same time!
You can easily see which language you are in by looking at the language bar:
You can change or disable the keystrokes by right-clicking on the language bar and selecting Settings:
Then select Between input languages and click Change Key Sequence:
If you have fat finger issues like me, you probably want to select Not Assigned.
So next time you find something that seems like a bug, remember, it just might be a feature!