Dave, I love you man, and you're a super genius. I really mean that, but you are incorrect on this. Anything that keeps an exhaust valve closed will indeed cause a backfire through the intake and carburetor.
With the exhaust valve closed, the cylinder still fires. Where else is the exhaust going to go? It will follow the path of least resistance back up through the intake and right out the carburetor. Seen it happen literally hundreds of times on different type valve train failures, mostly wiped camshaft lobes.
While it does not cause a miss or a dead cylinder, as that cylinder still builds compression and fires, it certainly disrupts the engine and makes it run rough and lose power.
You are correct that ignition problems can and certainly do cause pops back through the carburetor, but physical valve train problems can and do as well.
