I can confirm this also happening to me. If you have a not full stack of bullets in inventory, it will fill up, and all bullets unloaded from mag/ chamber after stack is full, will disapear. Also, dividing stacks of bullets, there will only be the half stack present, the other is lost. Update!- I tried verifying gamefiles, but problem still persists. I tried dividing bulletstacks also inhand and on ground with same result. It seems to me like the game is not able to produce a new stack of bullets in inventory.