As outrageous as it sounds, actually yes. This is a recurring code limitation that has been with Terraria literally since 2011, has been well known to the community at large for a great number of weapons and ammo combinations.
I may be able to find a solution for this particular weapon that does not profoundly impact balance, but we cannot "fix it all", not within the time available to me, nor was it something ever approved for me to do.
Any fixes to this are exceptions to the rule.
Edit: Went and took a look at this, and this weapon's stats were balanced AROUND this behavior. If I implement a fix for it now, the weapon immediately starts doing double damage . . .
That's not a good thing. Its not supposed to be doing that much damage. Its stats were built around the damage it currently does WITH the "lost efficiency" taken into consideration.
So if I rework it to not have conflicting immunity frames, I'm literally going to have to nerf it now, because the intended amount of damage was the amount it was doing before, and doubling its power outright is too strong.
So yes. "It is intentional that half of the ammo this weapon uses may miss (on a single target, mind you, multiple targets will likely be hit), because of limitations in Terraria's code, and the damage of the weapon was increased dramatically to account for the loss of DPS. If I rework it now, it will be TOO strong, and performing at UNINTENTIONAL levels of power, and we will have a bigger problem"
I'll see if I can fiddle with the mechanics enough to avoid such a problem, but I can't make any promises.