Easier to see in practice than to describe - blockers and force fields just knock a climber off, but a wrong-direction splitter has some... interesting results.
This is a blatant glitch with obvious intended behaviour so there is no need for discussion here - it will be fixed in V12.11.X (I considered including it in V12.10.X, but this is risky with such little time left until stable release, after all, it's a physics change, even if it's only intended to affect a very obscure edge case). I would be very surprised if the fix affects any levels other than those (if any) that specifically exploit the glitch, which of course I have no qualms about breaking. I've already implemented the fix in commit 6a70721.
