Turtle Siege Enhancer 3 cannot utilized already loaded ammo

[JDub.1530]

If you equip the Turtle Siege Enhancer 3 (I'm unsure about lower tiers) and board someone's turtle with already loaded ammo, it shows the correct amount count on your buff bar, but the skill ammo count is zero. If the ammo count increases while you're in the gunner seat, the ammo count of the skill increases as it should, but already stocked ammo is inaccessible. Boarding a turtle with 5 ammo already loaded means you can't ever shoot from the gunner seat (since it won't gain anymore ammo charges).