Item display does not render filled maps correctly while on display entity

The bug

When placing a filled_map in an item display entity, the item does not render as a map. Instead, the item texture is displayed. This happens even when an item_display value is used that normally should render as a map, such as fixed.

How to reproduce

1. Create a filled map and note its map ID
2. Summon an item display with the map in it.

   /summon item_display ~ ~ ~ {item_display:"fixed",item:{id:"minecraft:filled_map",Count:1b,tag:{map:1}}}
   

3. Observe that the map renders as a normal item, and not as a map