Crouching with item causes it to go up arm

I was playing Creative Mode in the latest snapshot (14w21b) and was making a video about an enchanted stick (no idea why) and as I was crouching/ sneaking in third-person view (F5), the stick was misplaced. It happens to every item and possibly blocks.

Steps to Re-create:
1. Get any item
2. Go into third-person mode (default F5)
3. Then hit your crouch key (default L-Shift)
4. The item goes up your arm instead of staying in your hand.

I have searched and found nothing like it.

EDIT
Thanks @Blah for showing me MC-46579. I didn't find it through my searching. This is going to be a duplicate