In Game master mode

1. Spawn US rifleman and US arsenal
2. Move the rifleman to the arsenal and open arsenal
3. By right clicking add 6 HE UGL grenades (they go to Alice standard vest)
4. By right clicking add 2 M9 pistol magazines (they go to Alice standard vest)
5. By hold/drag left mouse move the 2 M9 pistol magazines to the blouse/jacket
6. By right clicking add SB M14 magazines (the first 5 go to Alice standard, next ones go to blouse/jacket)

If you after the first 5 SB M14 magazines try to add another one by hold/drag method, the Alice vest is marked red with text "Volume exceeded" and fill meter is full and reads +6%

BUT if you change the order for 3 and 4 around (add pistol magazines first) then at 6 you can only add 4 SB M14 magazines to the Alice vest, and if you try the hold drag method Alice vest is marked red with text "Volume exceeded", but the fill meter is not full and there is no mention that it would go above (no + percentage).

I'm not sure but this may be related to the fact that, in this situation when you add the pistol magazines first, then when moving them inside the inventory, after the first magazine is moved, the remaining pistol magazine's placement in the Alice vest changes on it's own.

There must be other ways for this to happen, this was just one example.