'oh no...we both died...hurry and hit your button so we can keep playing...oh...crap...'
Yeah, I get it. It's just infrequent.
Once is far too much. Happened to me twice the first day I played mame (with my brother on his hotrodse CP he just pulled out of the box). Neither of us knew what happened the first time, but the second time on a different game got us both pissed. Almost made me think "Screw it, mame sucks, great when playing but dies at the best point, they must be doing it on purpose, I won't play it again". But luckily my brother found that it was P1 + P2 start combo that did it, unmapped it, and well, I'm still here.

I will
never, NEVER, ever make a CP where exit can be activated with just normal buttons.
A single button is too easy, too.
P1 Bottom 4 buttons and start=exit (I told you I was paranoid)
Ahh, okay I take it back. I
might do a "just normal button" combo, but your paranoid is not quite enough for me. I'd do P1 four buttons + P2 four buttons + P2 down right diag (grabbed by thumb). At least nine fingers needed, and the only reason P1 wouldn't need to do a direction is the stick is not where my thumb is. Serious. Otherwise at least two admin only buttons, at least one used only to exit, away from all other buttons.
But that's just me.

If it doesn't bother others, shrug.