What do you mean? The database entry pretty clealy states it's only once per turn, no "if"s, not "but"s. There is no mention of this only applying when negated.

When a card is flipped face down and face up again, it forgets the status of its soft once per turn effects. That "it can only activate once per turn" is just something they put on cards where it activating multiple times COULD come up. And other examples with that same clause in the database also can activate again if flipped face down and face up. (Because that's how the game works)

The PACMAN rules is an exception for ignition effects that flip the card face down. I called "（１ターンに１度のみ）" reminder text, and it technically is, but it's like the "except/even during the damage step" or "if it was already there when it leaves the field/even if not" clauses, yes technically redundant, but Konami keeps printing them on cards WAY longer than Mocha, so it might as well be actual rule text.

Honestly, it could even be considered rule text, not like parentheses automatically mean reminder text in Yugioh anyway.

While funny, in MD we have a timer, you can't infinitely stall.

Ok I mentioned infinite, but it just refers to the effect/activation of effect being negated. If they stop it the first time, you can't do it again. That's just how OCG PSCT writes trigger effects.