The brake piston in the caliper is on one side, so one side push, one side pull. Probably your brakes got uneven pressure. Your mechanic should try clean and oil the floating pin....Regarding the brake pads that has been taken out, my mechanic said that on one side of the wheels, the pads are still thick while on another side, the pads are almost worn out. But the brakes are not jammed at either side.