Maybe it's Sunday and I'm not really awake yet, but...
There's a beautiful, long, complete article about Berlin: http://en.wikipedia.org/w/index.php?title=Berlin
However:
http://en.wikipedia.org/w/api.php?action=query&prop=images&titles=Be... No images
http://en.wikipedia.org/w/api.php?action=query&prop=links&titles=Ber... No links
http://en.wikipedia.org/w/api.php?action=query&prop=extlinks&titles=... No external links
Likewise, no templates and no categories. Backlinks ("what links here") works, though.
Now, I followed a link to [[Berlin-Schönefeld International Airport]], and looked at "what links here", and there are lots of articles, but [[Berlin]] is not there.
So it's not a problem with the API - the information apparently wasn't stored in the database in the first place.
This will probably be updated on the next vandalism edit ;-) but I have to ask: is this just a fluke, or do we have a problem?
Magnus