In my experience it is not normal for any motorhome I have dealt with...and thats a lot. Typically once you push and hold the dump switch the coach will drop 3 to 4 inches in less than 30 seconds. In some (not all) extending the jacks triggers the same process. In my opinion a signal is not being sent to the dump valves on each bag from the Power Gear or HWH leveling brain. Note, I am not an expert, just spend a lot of time in and around motorhomes in the course of my work and lifestyle.
Good luck with the fault finding. Please let us know how it works out as this kind of info is valuable on a board like this.
John and Angela