just in case you didn't try it...did you adjust the barrel adjuster so the yellow (or red?) lines match up? my bike doesn't always shift properly and sometimes it's the adjustment, and sometimes it's the shifter (it isn't quite in gear), and then sometimes it's a mysterious external force i can never hope to comprehend. but it definitely flings my feet off at odd times when the bike doesn't go into gear. maybe yours is the same.