Map sometimes shows "unknown map" when not in the player's inventory

The bug

As can be seen in the screenshots, the map says "unknown map" in the chest's inventory and has actual information, when in the player's inventory.

How to reproduce

1. Get a map and right click it to make it a filled map
2. Put it into a chest
   → Map still has its information in the tooltip
3. Leave and rejoin the world
   → The map's tooltip says "unknown map"
4. Move the map into your own inventory
   → The information becomes visible again