The insides of entities are rendered again

Likely due to the fix of MC-161394.

When inside of another entity, the inside faces of said entity actually render now. There's probably no need to render these inside faces, as they're usually not visible in the first place unless your head is inside the mob, and blocks don't render their inside faces either.

This was fixed throughout most of 1.15's development but has reappeared in the latest prerelease. As a result, it has caused MC-130732 to reoccur.

This could be fixed by reverting the pre4 change, and making skulls instead use a normal block model instead of rendering as a block entity, and by having it use a second defined inside texture for when equipped on mobs.