I mentioned this in a recent bug report to Larian, and their support team told me this is a known issue intended to be fixed for full release.
Of course, if they don’t change free swapping between melee and ranged weapon sets too (which I hope they will), then people will still be able to get the AC boost by swapping back at the end of their turn. But at least we’ll be able to avoid the effect if we want to.
Yes, I don’t see them fixing it. It would require rethinking of the system, rather than creating two slots that player can freely switch between.
But who know maybe they have seen the light, and realised there are benefits to having, for example, multiple melee weapons of different damage type.