When someone have smershvest and buttbag attached on it , and put the vest+bag into their inventory (cloth,bag,etc) , we use a 2x4 shoes as reference . when player have no space for the shoes , still can simply take the shoes and magically into the buttbag.
And after that , if that player take the smershvest w/ buttbag on their hand or drop it on the ground , the smershvest cannot be take back into inventory due to the cargo space is not empty.
This issue could make player use for take more loot than his/her available inventory space , since the vest is only 3x3 in inventory, and buttbag have 4x6 cargo space.

1.grab a smershvest and put buttbag attach on it , keep both inventory empty.
2.put the vest into inventory and make sure you have no more inventory space .(I put it into a jeans and i have no more other cloth or bag on me)
3. look on the stuff on the ground , make sure it's bigger than available space (I use a hatchet 2x4 , and a dressshoes 2x4)
4 a "take" button appears , you may take the stuff and it goes into the buttbag.

Issues rate : 100 %

Note : stuff can only goes into the buttbag, and never goes into the vest itself
and I test without any mod , this issues still happens.

Make the buttbag no longer can be used as magical lootbox.