Dual-Wielding Issue

Duel-wielding with two swords isn't working, but I can use a bow and a sword?
Logged in and the first thing I wanted to do was trying duel-wielding. I first tried a shield and a sword, then a bow and a sword and they both worked. Then I tried to use two swords, the sword in my main hand worked fine. but the other one didn't move at all.

What I expected to happen was...:
When using the duel-wielding ability, I expect to be able to use both of my swords to kill mods.

What actually happened was...:
Was trying to use my swords for Duel-wielding to kill mods, but only the one in my right hand would do anything (it was like I only had one sword) The other one did nothing.