During rapid prototyping, I have been using CTRL+- to navigate to previous location in my C# code. However, once in awhile I accidentally hit CTRL+0 instead, which seems to switch to F# program. This results in destructively modifying the entire source file, which cannot be undone. Even if you manually switch back to C# program, the code is still broken. At this point the only choice is to restore the file from backup or hand-edit back to corrected for the language switch.

It really should be possible to simply hit 'Undo' and it should restore the file as it was prior to the accidental language switch.