This is not a Marble error but error in Openstreetmap database. I looked the map data and there is lots of overlapping/duplicate roads that some are missing the connection between them. I tried to clean it up but noticed that the area where this problem exists is big and the task is a bit more that I'm willing to spend my time... However, I think I did correct it enough so that once the database is updated your routing problem is gone. If you are interested in fixing similar problems in this area, you should consider opening account at openstreetmap.org and edit the map by yourself. It is not that difficult when using Potlatch tool that works on any browser with Flash. (The tool launches itself when you click the "edit" tab.)