read pinheads post again x2
heat expansion should not cause brake pressure
the fluid should flow to the master,
a residual valve is needed to hold any press in the line and once it built above that it should crack and relieve it back to the master
unlikely a bad residual but you could check but a piece of garbage in the line could block the backflow into the master
most likely you are not understanding the adjustment process for the rod though go back through the FSM procedure for that
let us know how it goes