Automatically equips lowest stack of arrows on scouts upon looting or when quiver is empty. This is done to save bag space by using up arrows that drop.
As of v2.0 Arrow Persist will automatically equip a Rune Catapult or Rune War Bow and make arrows then re-equip your main bow if you run out of arrows!
As of v2.45 Arrow Persist will automatically equip projectiles on rogues in the same manner as arrows for scouts as described above.