Faceted navigation after news search yields erroneous page

To reproduce:

• Go to the english Go Green website
• Go to the "News & Events" section
• Under "Show news from..." in the "Free text" search box, enter "solar"
• The results of the search are shown
• Under "Show news from..." click the category "Solar power"

Expected result: Results with the work "solar" in the category "Solar power"
Actual result: The page as in the screenshot. The location is:
http://www.demo.test.onehippo.com/news/faceted/News+Category/Solar+power?query=solar?query=solar