Mouse Buttons Backwards

I've scoured the forums, but so far have yet to find any info on why my mouse buttons in Sins don't conform to the setting I have chosen in Windows. As a lefty, I have switched the Primary click to the right button, yet Sins forces me to left click Menu buttons.

Why?

Only time I had experienced this in the past was with the rather poor port of Dead Space.

As someone new to Sins, I'd really hoped to give it a try, but if I have to retrain my clicking (>.<), I think I'd prefer to return the game, as that's a rather basic flaw.

TIA.