Simple bug.
Arbalests can still use their Sub-Weapon after using a cannon skill via basics and weapon skills that utilize them. Despite them being on a reload mechanic.
Don't think that's intended.
While not exactly contributing to bug report details... I do want to say that while it IS a bug, it's also one of the main things keeping Arbalest relatively fun to play or competent at all in PVE & PVP.
I'd argue that a lot is taken away from a class that already has little going for it if this were to be hypothetically fixed.
Not trying to turn this into a Balance Fu thread, mind, but personally I'd vouch for it to be made intentional with that in mind, because bluntly speaking I think the class will suck if this mechanic were to be removed. Obviously the decision is yours though, Dev, merely dropping in two cents on how the "fix" would very negatively impact it.
This is one bug that makes Arbalest very much viable in its current state, I would like to see this interaction taken away in an eventual rework. But for now if you take this away you're leaving Arbalest with quite literally only 2 good skills. (Buster Cannon and Heavy Tackle.)
But I do agree with Fern here, taking this away would devastate the class more than it already has been by the changes to the interaction with pushing enemies across tiles.
You know, it would be funny if arbalests could swing the chain to hit things with that weapon before its reloaded