"It wouldn't surprise me if, on paper at least, being compelled by the government to pass out of the area not requiring a visa was not an immigration offense."
So I'm not entirely sure how this squares up with my anecdote, but flying from Sydney, Australia to Vancouver, Canada (did, at some point) require stopping in Honolulu to refuel and take on passengers.
At that point in the journey, passengers were (are?) required to get off the plane and pass through US immigration to continue their flight on to Canada. I know of at least one passenger that was refused passage through US immigration at that point (even though she was forced to go through it and her final destination was not the US) and so she was not allowed to continue.
Like I say, I don't really know how that quite squares up with your comment, but I thought it was "interestingly similar", maybe?