Donuel, I've run into that problem repeatedly, and it's infuriating! I think it's the key with the "windows" symbol on it that's between the Ctrl and Alt keys at the lower left corner of the keyboard. Or it may be the Ctrl or the Alt key. Anyway, my little finger accidentally hits whichever damn key it is, when I'm meaning instead to hit the Shift key, and all my writing vanishes!

One needs to very carefully govern that left little finger to prevent this from occurring.