Follow-up on the trigger. Just as I suspected. The following quote is taken from an on line review by "The Texaner", Austin, Texas;
"This grade also uses a single-trigger mechanism that I've never seen before. When I first got the gun home and assembled, I tested the trigger in dry fire. The first pin fired just fine, but the trigger wouldn't set to fire the second barrel. Worried that I'd bought a defective gun from a store 100 miles away from home, I hit Google to see if anyone had experienced the same problem. Sure enough - yes. Apparently, the trigger mechanism uses the recoil from the first shot to set the trigger for the second. Weird, but as long as it works, I'm OK with it. Incidentally, you can get the trigger to set for the second barrel in dry fire by cycling the safety."
The part I hadn't figured out on my own (yet) was the fact that the lower barrel can be fired in dry fire by cycling the safety. Who'd a thunk it?