[Typo3] strange indexed search problem

[Oliver Schröder]

Hi list,

I added a hard coded input field for the indexed search to all pages:
<form action="index.php?id=254" method="POST" 
name="tx_indexedsearch">Suchen nach:&nbsp;<br />
<input type="text" name="tx_indexedsearch[sword]" value="" 
class="tx-indexedsearch-searchbox-sword" /><br />
<input type="submit" name="tx_indexedsearch[submit_button]" 
value="Suche" class="tx-indexedsearch-searchbox-button" />
<input type="hidden" name="tx_indexedsearch[_sections]" value="0" />
<input type="hidden" name="tx_indexedsearch[pointer]" value="0" />
<input type="hidden" name="tx_indexedsearch[ext]" value="0" />
</form>

But it doesn´t work, see: http://www.euronatur.org/cms/ (field in left 
column)

If I add "<form></form>" in front of that code, it works, see: 
http://www.euronatur.org/cms/Wolf.50.0.html

Is that just a strange problem or can´t I see the obvious solution?

Greetings
Oliver