The bug

If minecraft:barrier, minecraft:structure_void or minecraft:light are assigned models which contain visible cuboids, these will not render in-game.

How to reproduce

A resource pack that points barriers to the redstone block model, structure voids to the diamond block model and lights to the gold block model is attached. It can be seen that this correctly affects the block_marker particles displayed when held, but otherwise does nothing to make these appear as full cubes.