CurlyDave,
Quote from CurlyDave...
"The real problem comes on the implement side where the shut off valves in the connectors allow significant build up of hydraulic pressure in the implement even when it is detached. If the temperature increased while the implement is not attached depressing the check valve can be a real struggle."
I had the same problems, too. Now, I just connect the male and female connectors on the implement to each other when not in use. Then, if the temperature increases, all stays equal in the lines. The ends stay cleaner, too (if you are not using those rubber hose end connectors).