Well, sounds like you took the car to a Midas, bummer for you. Did you know they make all the money on parts. They told you haw bad those rear calipers where, how they could not "reset" the caliper by hand.
Why don't you try the parking brake. Put your foot under the pedal while it is not engaged. If it flickers or goes off, sounds like they adjusted something they should not have. FYI; Rear brakes have no pad indicator.
Or, you could have air in the line, and the differential valve is indicating that.