Falling blocks and minecarts displaying a block do not render inside faces of transparent models like they do in normal block form. For example, slime blocks and honey blocks do not render the inside cube's faces when viewed. Likely related to MC-164111

Reproduce Commands

summon minecraft:falling_block ~ ~ ~ {NoGravity: 1b, BlockState: {Name: "minecraft:slime_block"}, Time: 1}
summon minecraft:minecart ~ ~ ~ {NoGravity: 1b, CustomDisplayTile: 1b, DisplayState: {Name: "minecraft:slime_block"}}