Yes that’s weird indeed! And that’s what I thought at first but doesn’t work at all. I got surprised see that ROMs working on imame4all…
In advmame runs but horrible slow. Is not an option.
So, I just did what you said, disabling hotkeys and still can’t enter to mame menu pressing coin + start.
It’s a shame but it seems that option it’s not available in imame4all libretro core.