I had this happen even after changing out the Anderson 4-way 'Kantleak' valve cartridge several time... so I installed a water line 'cutoff' handle between the valve and the water tank inlet. No more 'ghost' filling, but just have to remember to turn it ON when using the city water FILL or using the water PUMP.
The Turners 2014 Thor Palazzo DP 33.3 35' Bunkhouse
BlueOx, '14 Ford Fiesta, DishHD, KingTailgater2, WifiRanger
50k+miles, 200+ parks, 47 states&Canada provinces, since Aug'14