Climber at checkerboard ceiling: inconsistent ascending/falling

[SimonN]

Lix 0.9.44

The 0.9 physics have inconsistent behavior when a climber approaches a checkerboard pattern -- blocks diagonal from each other -- at the ceiling. Look at the gif above:

• Green hits its head at the ceiling and falls, but
• orange ascends through the checkerboarding pattern.

Both lix are runners. Differences: While approaching the wall that we're about to climb, orange jumps over the bottom of the wall. Green does not. The exact location of the jump matters.

Source replay: climber-checkerboards.txt

I believe that both lix should fall. None should ascend through the checkerboard pattern. Checkerboard connections between terrain pieces should be consistently intraversible. Compare: We don't have downwards checkerboarding for walkers either.