When mouse is set to left handed mode, while in game, mouse works as expected, primary button shots, secondary zooms, etc. When in a menu, mouse goes back to acting like a right handed mouse, which is being held in the left hand. This means (for me, the left handed user) the primary button now acts as the secondary, and the secondary as primary.
This happens in all menu's, be it the settings, or the inventory screen.
Best way I can describe it, whether its case or now; is while in game (running around, looting, shooting, etc...), the engine is detecting that windows has switched the mouse buttons, and acts accordingly, but the menus do not, or their interactions are hard coded to right click / left click, opposed the the windows bindings?
Again, not sure if this is the case, but how it "feels".