Site search is broken

The site search in the header is broken. To reproduce:

1. go to http://qt-project.org/
2. enter something into the search box on the top right of the page and click "search"
3. this redirects to http://qt-project.org/search?search=qapplication

The result displays

GTE Cyber Trust Root.Us

within the text box to enter the search for Google. If you change that text to your actual search string, the results are ok.

The same happens if you do not enter anything in step 2.