Correct, the 4 piston system has more "drag" then the later style single piston cal's.
Although tight, should still be able to turn the rotors by hand.

Can they be turned now?
If so, press down "normally" on the pedal a few times.
Can they still be turned?
If not, something is keeping the the pressure from releasing.
Start at the brake hoses themselves and work your way back to the mstr cyl.

Unless the caliper piston springs are to long, i dont think that would be the prob. But never say never.
Another thing could be the pistons are "rocking" in the bores and sticking. Not backing off(cylinder bores to large).