Weird, I have this same DHGate Mobius Matrix and get blowback. I wonder if it's variations in the manufacture or just draw technique.
When you stop pulling, the water levels in the chamber and downstem equalize, displacing the air that was in the downstem. The air is ultimately pushed up...
Haven't seen this anywhere and maybe its super obvious, but I cut a random SS screen and popped into the bottom threads of the ShowerHead and it completely eliminates blowback of the bits of flower. Not sure if the WE or VRod have the same threading. But I'm super pumped because blowback was...