I was playing Minecraft 1.5.1 the lastest update and when i was turning my diamond in the item frame on the wall it turned darker but when it was right side up was light again.

Put the summary of the bug you're having here

What I expected to happen was...:
For the items on my frames (spawn pig and diamond)to turn without changing the brightness

What actually happened was...:
The brightness when the items turned were darker then what the item was right side up.
Steps to Reproduce:
1. Get an item frame
2.Put it on any wall.
3.Then put a spawn pig or diamond in it and turn it three times untill it's right side up.