Overlay-type connected textures (specifically overlay_fixed in my case) do not appear to work on non-full blocks. Here I am attempting to make mossy cobblestone colored based on the biome via matchTiles; this works fine for the regular block, but not for stairs, slabs, or walls, which end up rendering either a singular floating copy of the overlay above the block or nothing at all.

This is intended behavior that matches OptiFine but I plan to add an option to allow this eventually. Changing the behavior unconditionally will break resource packs that depend on it.

Don't know what kind of pack would depend on this clearly broken behavior but I suppose it's worth keeping around as an option