That's right, I started a new game, and I have NEVER seen the 2 weapons sheated when I use dwal wielding, for example, If in my right hand I have an axe, and in my left hand I have a sword, when I press X to sheate them, only the axe is shown on my waist, and if the sword were the one on my right hand, then the sword is the one shown. But this time, I saw the 2 of them, it was doing the tutorial quest, and I was like 0.0 "how cool this looks"!. So I entered the battle stance, and sheated them again to see if that happened again, but this time it didn't work.

So my question is: is this a bug? or something triggered the animation of the 2 weapons sheated at the same time?. This never happened again, and it looked really cool.

The left-handed weapon has never been visible for me either when it is sheathed. That's interesting that it is suddenly visible, but I have no idea what would trigger it. I would be inclined to think that this is the way it should be and that both weapons not being visible is a bug.