Mercenary,basic bolt with scattershot possible bug?

Im asking this if its a bug or working as intended.
Basic bolt has a set of bolts in magazine 7 bolts.

Scattershot shoots additional 2 projectiles,but you get 20% less damage and attack speed.

When you combine it with Basic bolt every attack shoots 3 bolts.

A) You have total 7 bolts in magazine,but every bolt shoots 3 so total 21.

You shoot 3 bolts and in mag it should goes from 7 to 6.

B) But it goes from 7 to 4 then to 1 but when you shoot the last one you shoot 3 bolts,which is strange.
Now you would say it should work as B i would say that you are right.

Thing is combine the Scattershot with High velocity round if you have Dyad crossbow you ahve additional shot in mag so 2.

You would think that it would work as Basic bolt so when you shoot you use both bolts,but no in this instance you use one bolt but shoot three so you have 2X3 bolts in your mag.

The question is which one is the corectly working and which is not?