The item frames I had already placed appeared to have random items in.
This I realised could be fixed by breaking and replacing it or rotating the items.

How to recreate it:
1. Place an item of any kind in an item frame
2. Change resource pack
3. The textures now go all funny and can be fixed by rotating the item.

This is not just due to the resource pack as it does the same reverting to the default pack.