To the contrary, it (or at least something similar) should work as far back as V1.15 or so, ...

Oh, time flies...

It would be straightforward to patch out -- the alternative is to make bashers stop when they hit steel/OWW in front of them, always, and so they would never move upwards. That's the behaviour I would prefer, but the devs already decided they prefer bashers to be able to move upwards.

Given completely free hand in designing basher rules, I would probably disallow letting bashers moving upwards, too. But if we would change that now, this change would probably break more levels than all the old-to-new-formats changes together (including non-solid ceiling!). So it's not so much what I (or namida) prefer, but more about how to move forward with what we have.