This has more to do with Piratez and X-Com Files, but I think it applies in regular X-COM games as well. If an unit has both a melee weapon and a firearm in each hand, which one takes preference if it can use both? Ie: Storming an UFO, you place a soldier next to the door to hit Sectoids with reaction fire, but doing so makes them come into melee range of the soldier.
Do your units take into account the CQC rules from the mods mentioned above and therefore automatically choose to use melee? If they have a hand slot free, would they automatically use unarmed attacks instead?