very common are hoses internally separating and thus they act as a heart valve whereby the fluid is pushed down them applying the brakes yet when released the fluid cant return to the master via the hose as it's trapped due to the flap of rubber restricting the fluid return AND opening the bleeder while the brakes are "stuck" will relieve the pressure and prove this theory.
if then the brakes still didnt free up then the caliper pistons OR the sliding hardware are the next suspects.
if the pads were recently replaced and this syndrome sunsequently followed, I would re-look at the specific work performed...
piston frozen...Just re read that
... replace both calipers AND hoses.... just because they look good outside dont mean nuthing.
if a piston froze then its probable the fluid was not often changed and thus the hoses internally are also victim to the degrading fluid.... hydroscopic fluid and cast iron calipers and wheelcylinders make rust....oxidation... "es no bueno"