Feingold + Assault Weapons?

Why did Senator Russ Feingold vote last year to end the assault weapons ban?  A vote to extend the ban was voted on as an amendment to a gun liability bill, which ultimately went down to defeat, but what explains Feingold's position?  Does anyone know they story behind this?

http://www.senate.gov/legislative/LIS/roll_call_lists/roll_call_vote_cfm.cfm?congress=108&sessio n=2&vote=00024