I'm not sure if it has been fixed but the same thing is/was happening with pistols.
All special slot items should probably be tested to make sure that this gets completely fixed.

Pistols.
Knives in sheath.
Knives in boot slots.
Canteens.
Water bottles.
Chem lights.
Radios.
Grenades.
Muon detector on Namalsk.

Some of these I'm sure are not bugged but you never know.

I do not know if this is an issue when you swap to something other than a weapon that is big enough to let the swapped item take its place.

I can confirm that. Pistols do not place back to the holster when you swap to another gun that is placed in your inventory.

I have also noticed this. It is an incredibly dangerous bug to happen in the midst of a firefight, and should be fixed. Steps to reproduce:

1. Equip Chest Holster w/ Pistol that is assigned to quickslot.
2. Place Alternative Gun (not the Pistol in Step #1) in backpack or clothing slots which is of same or greater size than pistol, but which is of the type that cannot be placed on back/sling slot.
3. Assign Alternative Gun to quickslot.
4. Place Rifle on back/sling slot and assign Rifle to quickslot.
5. Fill remainder of backpack and clothing slots and back/sling slots with items.
6. Press quickslot key for Pistol in Chest Holster such that Pistol is brought to character's hands.
7. Press quickslot key for Alternative Gun such that Alternative Gun is brought to character's hands.
8. Press quickslot key for Rifle. Observe how the Alternative Gun remains in character's hands instead of moving to backpack like it should. Open inventory and Observe that Pistol was not returned to Chest Holster, but instead is in Backpack/Clothing slot where the Alternative Gun used to be.

Once again, this bug is incredibly dangerous - I've had it manifest in a fight before.

Can confirm this also happend very frequently with radios too.

Yeah, I sounds like items which go into specialized slots designed for them (backpack radios, chest holster pistols, boot knives) in general all share this bug. The bug probably also applies to grenades and glowsticks.

I think it could be that the programming in the game performs a swap instead of returning the pistol / knife to their holster / sheath. I've noticed that when I encounter this bug, the handgun is in the space where the larger item used to be.

Is the severity of "None" intentional? This inventory bug affects everyone.

Was just not selected - but I think the Devs have an own priority list which has nothing to do with the public Feedback tracker

I would much prefer to have a reliable/predictable inventory management system (one that wouldn't get you killed or dangerously exposed in a firefight) than a new gun for next update...

Funny thing I have noted is that if the sheath is in the inventory (i.e not attached to the belt), with the knife inside it, then the bug does no occur (could not test with holster).
Not a workaround of course (what's the point of the sheath if not at the belt) but I thought I would report it nonetheless.

I think its in 1.25 allready fixed.

Thx Geez and Dev Team :)