How to change button in mame without causing infinite or

This is what I tried. I tried to change the button. Simple right.

I clicked on button 2 and then I press a button. Voila it works.

Now I double clicked P1 Button 3 Cheat. I want that to be a simple "Joy 1 Button 2"

Instead, Mame expect the button I press to be an alternative button instead of the ONLY button.

The interface is exactly the same. Pick a key and then double clicked. Is there a documentation somehow?

Note: I think I figured out. The first button I press after I open the menu will be the ONLY button. After that it's or or or. Strange interface. I wonder if it's even true. So the question still stand.