Thanks, there are currently 2 known issues with Prince Slime's ABN   attack and they're both related to recent changes to terrain collision, I think you may be referring to one of those:

1. On Space Highway (the 2nd stage), if you land a grab in the air you can throw the opponent through the stage via an aerial down-throw.
2. On any stage, but most consistently on Bridge of Tossing and Failure City (1st and 3rd stage respectively), if you and your opponent are below the stage and you throw them left/right inside the stage, they'll warp to the top while you SD.

If this is what you're talking about, thanks for reminding me, I needed to make a note to fix that for 0.6.0. If these don't sound like the same issue, lmk.

I like your proposed solution, it's much simpler than what I had in mind.

As a side-note, thanks so much for  your continued support of this game! It's really encouraging to see. Don't hesitate to let me know If you have any more suggestions/feedback, I'm always happy to see it.