If you adjust the amount of the linked ammo resource, it does not adjust the total weight for the character. Also, if you set the weight of the ammo to something less than 1, like .5, weight calculations will fail after you adjust the amount of ammo. For example: create a set of 20 arrows and link them to a bow with a weight of .05 each (per PHB). Fire one arrow, and it correctly subtracts the weight. Now add the arrow back by changing the quantity from 19 to 20. Fire again, and it will subtract the ammo but not the total weight for the character.
