For anyone wondering on how to fix this issue, this appears to be caused by some sort of interaction between steam and Kerbal space program. Right clicking on KSP in the steam UI and going to local files, then manually launching the game from the file system, should fix the issue. Or launch the game using CKAN. If the issue isn't fixed, make sure steam is completely closed down while launching KSP from the file system. If you are on Windows, creating a shortcut on the desktop to the main KSP executable may be helpful.
