Brakes apply themselves.

Make the dealer look again, and/or make the mechanic drive it until it happens. Or try another dealer. Your brakes are dragging. There is a 'reed valve' or 'flapper valve" that keeps the calipers from sticking, and when it happens on all four as you describe the problem is likely in the master cylinder

the master clylender has an adjustment from the booster if that adjustment is to tight it wont allow fluid to return to the master clyender resivour therefor its trapped between the caliper and master the dragging break createts heat which intern buildspressure in the line applying the break until it pulls the stearing or just strait stops the veihicle only bwhen the breaks are cooled down will it move or rod behind master cly has a little free play allowing fluid to get by orffice to the resivour