Front Brakes Locking On After Car Idles.

Brakes have been bled and master is a rebuilt unit. Nothing in brake system has been changed since car was driven with /6 setup. My son has driven this car to the Dreamcruise (5 hours from our house) 4 times last 6 years. It has been driven to the Tri-State Show in Penn 3 times as well as all over here in Ontario with no issues. This is the puzzling part. I appreciate everyone's input as many minds will likely solve this issue.