First I used the "Add anime to mylist"-function on the anime-page (since it's only one episode).
But since I got this strange result I deleted the file and re-added it with AniDB-O-Matic - same result as before.[/quote]
I tried again (with AniDB-O-Matic) - and now there is a new generic file in the list, that wasn't there before.
This file was added to "MyList" and appears on the MyList-page regularly - problem solved, it seems.