I changed the height of the character while creating one from the character creator. After using cape or equiping elytra on the character it doesnot lineup. Screenshot are below.

To recreate this bug follow these steps:

1. Goto Dressing room
2. Click on create character
3. Choose Select from character list and select steve
4. Goto Body>Size and change height to smaller and arm size to narrow
5. Goto Body>Arms and equip Prosthetic forearm on the left arm
6. Goto cape options and equip any cape.