Trailer air suspension deflated until?

Well, the air bags on a trailer I had the other day were not inflated at pretrip or after I went to fuel a couple miles away, so I screwed with the exhaust valve and a lever in there for like a half hour, trying every combination of building air and having brakes on or off, but nothing... then they were inflated when I got to where I was going (and it didn't sit all that low with them deflated so I wasn't too worried about rolling with it at the time). Looks like the operating instructions I found for that say it should work without moving the truck. I think it's a manual valve too, as it has the same type of knob as another one that worked manually.

Anyone had this problem, or is it a problem?