Well how i found it to work was this. If i added another pack inside the first pack i could then carry that pack with full items or even add items to it by right clicking the pack inside, Doing this would open that pack and i could add or remove items. Now to get rid of the extra pack all you do is pick it up and drag it out of the main pack and it drops to the ground.
I would not think they would allow this? And if it is a legit way to carry extra packs then my only concern is the fact that the packs inside do not carry over their weight of items inside.