All right... I believe we have solved the mystery.
We recently updated Unity, and Unity has apparently introduced a new feature (sic) which causes people who are not in an English-speaking country/not running an English native version of Windows to have this problem. It has to do with how it converts numbers to letters; the new version attempts to auto-recognize what language you're using and then changes the way the code works.
As we speak our senior programmer is fixing it. The next time you try it, it should work normally. If it doesn't, switch to the stable or beta branch and that should fix it too. Any progress made in any version will persist, so don't be afraid of using a different branch; you can switch over later. But it should be fixed by the time you read this (on Steam).
Thank you again for your patience, and sorry for the hold-up.