Problem With Air Valve?

[damnyankee36]

I noticed on my system with an Accu-air manifold, that when I release the pressure in the tanks, my bags loose pressure. With the tanks empty, the line pressure is low enough that I can remove the main airline to the manifold. Air then starts coming out of the "IN" port of the manifold.

Is this right? Since the tank normally has more pressure than the bags, I would imagine this would never cause a problem. I just thought the only time air should be moving is when either the lift valve or the dump valve is opened.

Maybe I need to see if there is trash in the valves even though I have a filter/water separator right before the manifold.