When I right-click while holding the crossbow, it loads the arrow as expected and holds it at ready.  Firing the crossbow with another right-click consumes one arrow from inventory, returns the crossbow to its unloaded appearance held to the side, but does not fire an arrow.  Doing this multiple times in a row appears to consume one arrow per attempt, but then switching to and then firing a regular bow results in all the missing arrows being back in my inventory.  Regular bow fires as normal.