I'm going fore-post that I havnt read this entire thread and that being a tank main Warrior is my least favorite of them all..
But looking at the data mine of the new skills you can see it on Reddit and it was posted on official forums a while back too.. the weapon dosnt just "disappear" it looks to me as if he sheaves it on his back.. you can see his arms go back with the weapon before it vanishes.. it may be that for the benchmark and the mine of the skill that weapons on backs are hidden and the weapon will just show up as if put away..
I could be wrong but that's how it looks to me from the animation