Tested on 2 servers over a decent period of time (I doubt de-sync)
Affects hotbar and inventory (Hitting tab and trying remove or swap won't do anything (Until you rotate))
Your character zooming in or free looking (alt) won't alleviate bug.
Items Tested:
Rags
Morphine
Protector Case
Double Blaze (attachments: fully loader snap, long range scope)
Repeater
Glow plug
Truck Battery
Splitting Axe
A FEW other items (rangefinder) might have been tested but either way, I only found those three items to be affected.
Hope this is useful in someway and it's interesting (to me) to see that character movement interfering with the hotkeys.
I'm guessing the new UI would of taken care of this but since it seems subtle, it seems worth mentioning.
Happy to provide more info or video if needed.