The shadow of any mob above a hanging sign is under the hanging sign! Including NoAI, and flying mobs! And, it happens in EVERY single 1.19.3 snapshot/pre-release. I not wanted to include every single mob in the screenshot, because I'm lazy to do it. I'm not sure if this is a feature request, but it looks awful.

To recreate:

Place any full block and a hanging sign above it

Summon any mob

Expected: There is no shadow of the mob or the shadow is thin

Observed: The shadow is on the block under the hanging sign