Quivers holding non-arrows
 

You can't put non-arrows into quivers manually, but if the quiver is the next bag with space available and you right-click loot something from a mob, the item will be forced into the quiver. This occurred with a tailored quiver (just in case it might not affect all quivers).

This happened in classic to, always to my amusement. Primarily with tiny or small items if I remember right.

A medium item fit into mine...Woven Cape

Fixed a while back.