The fact that you could dual wield two of the same weapon was the bug. I changed dual-wield a while back to use both the pounds and ounces when factoring in dual-wieldable weight, and screwed up the math with misplace parenthesis. I fixed it recently when investigating another bug.

I think it was a lot nicer to have it with the missplaced parenthesis. Only makes sense that you could wield two weapons of the same weight if they are light enough, for example, dont surpass 70% of your max wieldable weight?