Loading of script truncated, search form fails

In Opera 9.5 (Mac OS X 10.5.2, build 4716) the search form of

www.kieskeurig.nl

does not properly function.
When I choose a product category behind the blue 2 in the top, fill in a  
search term behind the blue 3, and press the "Zoek" button, I get the
same  
search page again, instead of search results.
The search is performed by a javascript DoSearch() function.
Trying to load the script file that contains the script search function

(http://www.kieskeurig.nl//nl/product.nsf/default.js)

also fails, the file is sometimes truncated in the middle of the DoSearch  
script, other times it seems to load, but then searching for the term  
"DoSearch" brings me to the ultimate lower right corner of the window,
 
without showing any text, just white space.
This is weird behaviour of Opera. The page is not valid, but Safari does  
not seem to have any problem with searching, and with loading the script  
file in the browser.