The serviceman was stumped by it. He said he has never had anyone else with an issue like it. He hoped a good cleaning would fix it, but that hasn't been the case. I thought I would ask a wider audience here to see if anyone has had something similar happen. I have had the machine for 4 years and this is the first issue I've ever had.
I'm also no where near the knob when it happens. I lift the foot, turn the quilt, and then sit back and watch it drift. I put the foot back down, readjust the knob, and go on my way. If I could remember to check each time I lift the foot, it wouldn't be such an impact.