Now that all this was cleared, I had a moment to play it, and it's a great game.
I fully understand why the higher levels don't have different maps for the various difficulties, but also found that solving The Bridge (again) didn't register for higher difficulties...
At first I didn't see that there are a few more levels, so some indication like a scrollbar or arrows pointing down (and up if the view is showing the higher levels) would be useful. And an "official" Quit button couldn't hurt ;)
(Also "Back to Menu" and/or "Restart" for within the level)
But that is small stuff that's easy enough to add for an update :)