Character consistently drops magazine when starting reload on the ground and pressing 'B' to move into crouched position before or shortly after reload animation is finished. This doesn't happen when moving from crouched to standing position while reloading.
This happens on 1.14 stable and 1.15 experimental and is reproducible. Most of the time it drops to the ground, but it's been put back in my inventory too one time so far that I've noticed.