2017 Wabash air backfeed? Check valve? Pressure Protection Valve?

When I set my trailer brakes I get a big blast of air backfeeding into my truck, almost like the trailer's air tanks are emptying out of the red glad hand back into my truck's system.

It actually causes my trucks brakes to not set if I pop both valves at the same time until most of the air seems to bleed out of the trailer.

There seems to be a pressure relief valve on the inlet side of the trailer's air tank, I'm wondering if that has gone bad? Is there a 1 way valve somewhere on this thing?

Also, the button you pull to inflate the sliding tandem bolt release will reset if you don't sit there and hold it until what seems to be the majority of the air is dumped from the system.

Is it that little valve on the side of the tank that has gone bad? Part # is VS-1128 Pressure Protection Valve

Would this cause these problems?

 

VS-1128 valve sits on the supply side of the air tank from the looks of it, seems to be the only valve I can see between the truck supply and the air tanks on the trailer.

This is the only trailer it does it on, I've pulled 2 others, so not a problem on the truck side I assume.