I finally picked up an SM3, the last machine on my "want to try" list. There is a small tab on the underside of the carriage that hits the left side of the body when the carriage reaches the center point when typing. Not sure if something is bent or if its just a slight adjustment. Pressing the shift key even slightly lifts it over that catch point. I haven't looked every closely at it yet and can post a picture later if necessary.