having a stack of 100% ammo i tried to put it into a stack of 81% ammo and it turned the 81% to 100% but made the 100% to 50%, therefore i lost 30% worth of ammo

Okay it looks like this happens when you right click to split then overflow the stack you are dropping on. For now I would be careful to left click drag if you intend to combine stacks. Nice find, I'll get a fix out later tonight.