When playing on a server, I noticed an issue with hit-boxes. The bug appears when you enable visual entity hit-boxes. When you enter 3rd person mode, your player's hit-box is above the player. The only part of the player that is in the hit-box is a small part of the head. This also appears above the player in the inventory screen.
Steps to Reproduce:
1. Press F3+B
2. Press F5 or open the inventory
3. Look above your player
This issue has been reported already. It has been linked to the original bugreport.
Please search before reporting any bugs, as it's likely that one exists already.