Power 2he weapons turn invisible if you disable the vanity weapon slot or they both (your power and vanity) apply at the same time. The only way to make it show is disable the vanity tab all together.
Sometimes disabling your off hand vanity weapon also disable your main hand slot in your weapon switch.
I confirm that ! i had some unwanted things happen on my barb ending with an invisible 2h sword !
My staff on necro has the same bug atm. Disabling vanity tab makes the main staff visible again.
Also, another bug is that there are some items that have no standard Weapon Type on them, I will link a picture for them. What Item Types are those linked to?
morphs have always made strange effects !
Yeah, and I thought, this is as good as time as any to address it 
Who knows…