It is random, they don't react on your attacks.
OK. Classic paranoid perception.
but the lag when opening large bags can be unpleasant during combat.
Idk what causes the lag, but if the items were being extracted slowly one by one, the gameplay of opening in combat would be even more exciting (dank).
Remembered one more thing - I tried to bind thumb buttons (Mouse4 / Mouse5), but it did not work.