Versions

Betweenlands version:

3.6.1

Forge version:

1.12.2-14.23.5.2847

Singleplayer or Multiplayer:

Singleplayer

Installed mods:

Betweenlands
Phosphor
Optifine

Description of the problem

How to reproduce:

1. Right-click a Tamed Chiromaw (version doesn't matter) to make it sit on your head.
2. Try and hang it on a ceiling made out of slabs (placed on the top half).
   2.5 Place a second layer of full blocks with a one-block tall gap above your first ceiling.
3. Watch the Chiromaw ignoring the ceiling's collision (if followed 2.5)/flying away instead of hanging.

Expected result:

You should either be able to hang the Tamed Chiromaw on a ceiling made out of slabs placed on the top half part or being told you can't do it.

Actual result:

Instead, the Chiromaw won't connect with the slabs and will find the next layer where it can hang or just dismount from your head, depending on the 2.5 step.

Pictures:

This is intentional. The chiromaw will only hang from blocks that have a full/regular face at the bottom, which top half slabs don't.