Same problem but when I detached the hose and then turn on the water and then off I have no backflow spray.

I thought when the water spays out when turning off water the backflow preventer working release pressure in hose? I don’t replace mine till the water sprays out the reliefs holes when turn water turned on. When I have Spray nozzle on water hose and spray and release sometimes the backflow with squirt water. IMO this normal.