Weapon auto-switching after device use

Every time I go to use a device like a grenade or RPG, the weapon I was using prior to the activation of the device will switch to whatever is considered your primary weapon. In battle royal, what is considered your primary weapon is a mystery to me still, but I'm guessing the first map weapon you pick up, but either way this messes you up especially if you just switched to you secondary because your primary's mag was empty and then decided to throw a grenade and then you get auto-switched to an empty weapon mid fire-fight.