The demo version has been hot fixed as promised. The level "The Underedge Pass" should now be available to unlock & play as it always should have been the case.
Note that both full and demo version players can play this level seamlessly with each other. Demo players can also purchase items from The Smuggler's Den, which is directly available after the Underedge. Of course, The Underedge Pass isn't exactly the best source of Gems income.
Anyway, sorry for the inconvenience and the confusion.