As stated in the Summary, if you interact with any kind of Container (Weapon Box, Dead Body) while having any Launcher equipped and attempt to take a Primary Weapon to replace your current Primary Weapon, your Character will automatically Equip his Sidearm instead of Equipping his newly acquired Primary Weapon.

This seem to be a bit unnecessary as in general you would equip the new Weapon that you Picked Up, not switch to your Sidearm first before having to switch back to your new Primary Weapon.