There are a few features that belong to two or more countries (mountain passes at country borders in my special case).
Since the country is automatically assigned and it is not possible to assign two countries to the same feature, obviously the only (and IMHO worst) solution seems to be a duplicate entry – or is there a better alternative?
btw: The same problem occurs with other administrative borders.
There is a field in the database to add additional countrycodes as comma separated list of iso two char country codes.
Today I made the field editable with the user interface.