Item Frames in Multiplayer do not know the NBT data of their stored item.
What I expected to happen was...:
Items in item frames should receive their NBT data from the server. An example would be if I put a pair of lovely cyan trousers in an item frame, they would appear cyan. Enchanted armor would shimmer.
What actually happened was...:
Items in item frames do not render according to their NBT data, colored trousers always looking brown and magic swords looking dull. Poking around with mods revealed that while Item Frames do know the item ID of the framed item (obviously), the client's copy of the item never has a NBT tag with color/enchantment data.
Steps to Reproduce:
1. Begin a game in Multiplayer.
2. Craft a pair of blue trousers.
3. Place them into an item frame.
4. If the bug is present, the trousers will appear to be undyed.