Preview not allowing cmd 0 for full size view

I don't know why but I cannot use the cmd+0 keyboard shortcut to get a full size preview of an image in the Preview app, the menu option works, but not the keyboard shortcut, while the magnifying options both work (less and more). I noticed this a while back, that it would work after manually using the magnifying options, but now it doesn't work at all. I tried using a custom keyboard shortcut via System Preferences, but that doesn't work and more tellingly it won't even change the menu option to something custom e.g. cmd+\

Anybody suffering from this as well?