I browsed the forum and found out through several bug reports that any asura using any piece of the Protean armor set (and not hiding it) causes any back piece to bug out. In this instance, the bug is for the Quiver of Swift Flight on my asuran thief.
1st pic is neutral with no Protean armor equipped.
2nd is Protean shoulders equipped, but hidden
3rd is Protean shoulder equipped and unhidden. Note the change in the back piece.
4th and 5th are Protean chest and Protean legs respectively creating the same bug.
