This is mere a Feature Request than an actual Bug
Switching from a Main Weapon (Rifle/MW) to a Backup Weapon (Pistol/BW) always leads to a ~3 Second long Animation of the Player Model putting the MW on it's Back and then slowly unholstering it's BW.
This makes not much sense in the Perspective of Simulating Real Soldiers Behaviours and also renders the "Weapon on Back" Key almost useless if not for Roleplay purposes only. {F17005}