When logging in, I have two spears on my Hunter’s back like a Fury warrior even though obviously only one can be equipped.
When in combat, one stays on back and unequiping/re-equiping weapon does nothing.
So far only unequiping everything and logging out and back in fixes it temporarily.
Dunno if it’s relevant, but using Draconic Gladiator’s Scythe transmogged with Headhunter’s Spear.