Comment 2 for bug 283128

I can confirm the same problem with a "Generic 105-key (Intl) PC" Keyboard model setting and "USA" and "Germany Eliminate dead keys" as the two configured keyboard layouts (using both shift keys as switching-trigger).

The interesting thing i observed is that after removing the German keyboard layout and re-adding it again. The keyboard switching behaviour is immediately returned to its original proper functionality and there is no sign of a 3rd ?/(null) layout entry ... After an unidentified period of general desktop usage the rogue 3rd layout crops up again.