Had the same problem 2 months ago. I was ready to take things apart and the problem went away. Yes I also oroginaly thought it was the lever mechanism not returning to the closed position and would let it slam shut. Once it solved itself the only reason I could think of may have been a speck of dirt on the valve seat.
Not sure this is an answer you can hang your hat on but if you do end up taking things apart the valve seat is the first place I would look.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles