I believe this was intentional and I personally think it doesn't need to be fixed. Since day 1, if u ever switched weapons you lost half of your ammo for that weapon slot. I've noticed lately that it doesn't happen to primary anymore, only special and heavy. The reasoning behind this is that people will abuse the ammo regenerating weapons. Anytime someone runs out of special ammo, the can switch to ice breaker. Now it still works but you only get half of full reserve if you switch from ice breaker to any other special weapon. But there's also the issue of, if your holding an exotic on a different slot (example: gjallarhorn) and u have to switch that to another heavy, wait for ammo regenerating, then switch back both heavy and special. You'd lose 75% of your heavy ammo by doing this. Its an incentive to keep players from lazily sitting around waiting for ammo. At least that's what I thought. Edit: didn't notice that this post was very very old.