LF kelsey Hayes caliper started dragging.

If the bleed port is open, how could there be any fluid pressure in the caliper? If there is no pressure, how could anything in the hydraulic system be the culprit (hose, tubes, MC, prop valve)? The only hydraulic thing I could envision is something locking pressure up on the side without a bleeder, maybe a piece of rubber acting like a check valve in the cross-over tube, or such.