Although the image
http://de.wikipedia.org/wiki/Bild:Hungary_budapest_city_park.svg was rendered
correctly when put into an article, it couldn't be viewed on its description
page and also not as a default thumbnail. A thumbnail bigger than the default
The author had to remove a lot of information from the file, to shrink the
filesize from 804.184 Bytes to 138.941 Bytes (See history). Only then the
default thumbnail and the image on the description page were rendered.
You could download the bigger version from the history
and upload it as a copy, to watch the effect.