Gunslinger does not gain stacks from using Barrage (Pocket ability 1)

[Skele₊]

When using Pocket's Barrage ability you do not gain a stack if you have Gunslinger bought.
All of their other abilities do work.

I tried several other characters and all of their abilities trigger it just fine.
Impossible to not replicate yourself, requires only the Gunslinger item and having their first ability unlocked.