Thank you – but my problem has been resolved. The problem is the text length limit in the tw.api of 140 chars. If you add text + url > 140 chars, the tw.api.php cut the url. So remains a piece of the url as text only.
Two solutions: 1. text length must be <= 118 chars + a url with max. 21 chars. Therefore you can use a “url shortener” like the google. 2. text length + url length <= 140 chars