Missing texture when equipping trimmed armor on a horse

To reproduce:

• /give @p minecraft:iron_horse_armor[minecraft:trim={material:"minecraft:resin",pattern:"minecraft:eye"}]

• Put this on one of your horses

Expected results: the missing texture would not be seen, as it should only ever appear if the resource packs in use are broken.

Actual results: the missing texture is visible, so something is clearly wrong with the default pack.