hmmm. i'm happy to say i don't know anything about these bikes but, it does seem as though that seat tube insert is adjustable and can be seen in swissbike models as well as in other models across the montague line. in every one of these pictures you can see that the extension piece is standing proud of the maintube by approx. 100mm which is minimum insertion length for bicycle seatposts. this seems like a dodgy arrangement since at 100mm the seatpost will not be inside the maintube and all the leverage is solely on the extension (as is seen in the op's pics).