This is NOT a in-game bug. This is only a texture pack model bug.
I expected the results or the rotation of the item in hand to be the same as 1.8.
The rotation defaults to the way normal items are held.
*Note: I used Cubik to model items. This may not be a bug related to the game but I added it just in case...
Models made by me.
Bottom: 1.8.X
Bottom Right: 15w32c
Resource pack format has changed:
https://mojang.com/2015/07/minecraft-snapshot-15w31a/