I ran into this problem as well with my intellimouse optical being recognized as an intellimouse web. I was able to change to optical by updating the driver, select "browse my computer for driver software," selecting "let me pick from a list of device drivers on my computer," unchecking show compatible hardware, and selecting Microsoft and "Microsoft USB intellimouse optical (intellipoint)."
The buttons are working correctly for me now.
I noticed this was a problem for many people looking and wanted to make sure that this info was available for future use.
Hope it helps.