[cleszkie]

Are you running rubber soft lines to the calipers? Have you replaced them recently? When these lines get old, the interior plies can delaminate and a flap will form. This can cause a blockage in the line that either won't let the fluid pressure release, or won't let the pressure get to the caliper, depending on which way the flap is positioned in the line. I've seen this before. Just a thought.