Intro-text not displayed for some articles

For some of my articles there is only a heading but no intro text displayed. The affected articles are (from my point of view) not different from the correctly displayed articles.

You can see this for example on http://www.chiagra.de/medikamente-bei-gicht/gichtanfaelle-behandeln/schmerz-und-entzuendungshemmer-wirkstoffe/diclofenac.html (bottom of page)

Regards,
Ulrik Andresen