Retrieving metadata seems to be mandatory
The reason was that their names could not be found when trying to retrieve metadata.
If I rename them providing them with names from known movies it works.
Unfortunately when unchecking off "Retrieve descriptive metadata" in the Console's library not movies will be shown at all.
And when I activate the button and try to deactivate the search for metadata in the 'Metadata' section of the Console no movies will be shown, either.
Is there a way to become independent of metadata at all?
Thanks for helping!