Ha! Interesting conundrum.
Analyzing the purpose of this rule:
- Prevent a player from taking advantage of an unintended one-ball multiball state.
- Trapping up is meant to safely detain the active ball(s) so that the player doesn't lose them while a tech frees the stuck ball.
- But in this case, trapping up may not be "safe"
My first thought is that the player should be allowed to attempt to transfer the ball to the other flipper to avoid the unsafe scenario caused by DI flipper attack. But then you run into the problem of a failed post transfer leading to additional single-ball play time in a multiball state, with the player having the ability to claim (whether true or not) that they didn't mean to collect that additional Super at QED.
I think I'd still allow the player to attempt a flipper transfer.
Note to self: when playing DI multiball in stuck ball situation, trap up on the flipper with the attack line that's furthest away.