Do you have the lines switched at the master cylinder? Aren't the front drums wider than the rear and carry a different dia wheel cyl ?
If what you say is correct and the pressure is relieved when you crack the line at the master cyl, then its a no brainer . Its the MC or the rod is too long . Can't recall if you have PBs , if so would the booster be screwed up ?
Just confirming what the other guys are saying .


Does the MC have a metal inserts where your lines screw in ?Check the end of the line and see if they align properly. I know if it was completely closed off both brakes would stay on but maybe brake springs could be a little weaker on the RF .