> I was wondering about this, what makes this so hard to emulate that on perfectly
> working games many times this is not implemented?
Because most games have asymmetrical visible regions, so emulating the flip isn't simply a matter of reversing the image. And things get weirder than that in Konami hardware. On those games, making the flip work is on a scale of "as hard as emulating the game in the first place". So all that combined with it being a feature probably 7 people actually use means it doesn't happen much.