Maps in item frames go dark when turned upside down or for other unspecified reason

What I expected to happen was...:
I expected maps in item frames to remain normal after rotating them and putting other items next to them.

What actually happened was...:
When turned upside down maps are darker; for some reason when I placed my enchanted bow in one of the frames, 2 maps went dark (see attached pictures below).

Steps to Reproduce:
1. Place an item frame on a wall
2. Put a map with discovered area into the item frame
3. Rotate it twice so that it's upside down