A friend of mine made the following discovery:
MySQL TEXT fields have a limit of 65,000 bytes. If you insert anything larger than that in to a normal TEXT field mySQL will silently truncate your data without telling you (meaning software checks are probably a good idea). MEDIUMTEXT will store 16 million characters and LONGTEXT can handle over 4 trillion, but this information does not appear to be readily available in the online mySQL manual (although it is hinted at in this table). SMALLTEXT has a 255 character limit. Something to bare in mind when designing database applications.
Answer to my initial problem is that I'v tried to add a (the first) bigger article, more than, say 300 chars. But, the real problem was the < sign in that article (eg. "They were offering some millions (<10) for a small piece of that company"). That was the sign that 'cut' the text after in my article.
MySQL AB :: MySQL Documentation MySQL Field Types
Thank you very much for replys.