The filename of the image had special characters in it (ü) .
What happened was that the filename was changed to regular characters (u instead of ü), and the text in the popup code lacked the characters, they were just left away.
- Original (local) filename was:
- After adding the popup image, (uploading from local computer) it changed to:
ruckbau-dusseldorf-5.jpg (Which is correct IMHO)
- The popup text showed:
[[popup file="2012-06/rckbau-dsseldorf-5.jpg" description="(thumbnail)" alt="Rückbau Düsseldorf 5" align="inline" ]]
- The used character set in the templates is utf-8
Of course I know that I can work around it by changing the filename in advance, but since this can also point to something which goes wrong, I decided to ask it here anyway.