See attached image.
Probably only relevant to the experimental version, though I didn't outright test if it happens in stable.
Glider shadows fixed again. The problem was the fix to the bug "Splatting lemmings mid-air" (http://www.lemmingsforums.net/index.php?topic=3005.0) in commit 7b046cd. The transitions remembered to be done at the end of the movement were ignored during simulation.