I do not know if it came with 2.0 or was present earlier, but dual wielding with an elemental weapon in main hand is broken, at least with the assassin.
With classic claws in main hand (physical), the second claw simply adds nothing damage-wise.
However, with an elemental weapon in main hand, when you put the second one (be it physical or elemental), you actually lose DPS. It's as if the second weapon disables the flat bonus elemental from the main hand (both the innate, and the free flat affix)
Edit : I will add that you ca see it directly on the LCS, but I tested it also by mesuring DPS on several bosses, and the loss in DPS is indeed coherent with the LCS