New glitch with the latest patch?...
Not sure why, but in multi (if that changes anything), all of partner's arrows in his skill bar are constantly removing themselves pretty much after a battle. His skills remain, but whether he puts the arrow in the 1st, 2nd, or 3rd skill bar, they're always disappearing on him.
Every time he wants to use a special arrow, he's forced to go into his inventory.
Also, if it's important to know, all his special arrows are in a backpack for him.