I can't change the key preferences settings.

I can't change the key preferences settings. I assign "0" (zero) as the back key, but it doesn't seem to work. I also tried changing another shortcut that I already used to 0, but that didn't work either. Even restarting the program.

To reproduce the error:
1) Go to the Preferences in Edit pannel.
2) Assign to the Playback ("Retroceder" in Spanish) the button 0(Zero)
3) Use the new assaigned button to see if works, but in the current version does´t work