Steps were in my case and have not been attempted with other variables.

2055 first person server
Kolt 1911 with pistol silencer attached to hotkey 1.
With a VIKHR currently equipped (not aiming), and in a "zoomed" view (mouse wheel held down), press 1 to begin the weapon swap animation and then immediately click down the right mouse to "aim" while also walking backwards.

This means you will be walking backwards, zoomed in, and trying to aim when the weapon is Kolt is first equipped. The character appears to go into a melee blocking pose for a short interval between the weapon swaps, and gets stuck in that pose when the pistol is out. This position can not be exited, and the gun can only be aimed at the sky. Character cannot run or defend itself.

Consistent bug that reproduces itself every time when following the above steps.