There are 4 solenoid valves - one for each jack. When operated, the electricity is applied to two valves at a time so that they operate in pairs. Once you take your finger off the button all electricity to the valves is gone and they should all hold their pressure. If two jacks are leaking back, then two solenoid valves are not holding it. It could be something as simple as a loose T handle on the valve. I've had that happen. Just tighten them up by hand. If they don't move, then it's time for some solenoid valves.
As Tom mentioned, HWH is a great company and they will help you out any way they can. Also, while your Winnebago has a 1 year warranty, HWH warrants their system for 3 years. I had a bad HWH slideout solenoid valve that allowed my main slide to come out when driving
and my 2003 Suncruiser was out of it's 1 year warranty period. My Itasca dealer replaced the solenoid valve under the 3 year HWH warranty so you should be covered as well.