brakes lock up in reverse

I had brakes and rotors put on my 1999 Contour yesterday. When I got home I was pulling out of driveway in reverse and appears brakes lock up when in reverse. If i take foot off brake reverse works fine so not transmission. If I touch brakes car locks up and won't go backwards, feels like brakes just lock up. What could mechanic of possibly done to cause this.

Only thing I can think of is they forgot to put one of the bolts back in that holds the caliper to the knuckle. This could cause the caliper to lift and bind when put in reverse. Have a friend see whats going on and see if a caliper is rocking back and forth.