Originally Posted by mconlonx

Could be the high limit screw on the FD is a bit too tight. Also could be the lateral alignment is not set up correctly.

If this happens when you start from a start, I'd assume that you are in the lower gears/larger cogs out back at the time. That crosschain type of situation could cause it, if you backpedal at all in one of the lower gears -- FD will auto-trim toward the inside, facillitating the unwanted downshift.

Could also be Shimano trying to retrain you with your shifting. When approaching a stop, instead of shifting into a lower gear out back, consider shifting into the small ring up front...