Rear disk conversion issue

My original suspicion with the master cylinder was improper assembly or a bad part from the manufacturer. I know of one master failure that caused the same symptoms. Did the brakes slowly bleed off from locked or did you have to relieve the pressure? About all the bad brake hoses I've seen show no sign of have unraveled internally, and won't show it until you try to force back pressure through the hose. You can usually feel the soft spot or spots when you take it off and start working it, though.