Locked maps go transparent when transferring between worlds.

I transferred a all white locked map from one world to another.

What I expected to happen was...:
The all white map to stay the same allowing me to use it.

What actually happened was...:
The map went almost fully transparent with the gray and white squares.

Steps to Reproduce:
1. In one world, create a new map.

2. Lock the map.

3. Save the map in your toolbar.

4. Take the map out in a different world.