MultiformeIngegno on "First page of search results is ok, the 2nd redirects to the home page"

Twenty Twelve child theme. Nginx 1.3.11.
When I visit http://luigisettembrini.gov.it/?s=informazioni the page is displayed properly, when I click on the link to see the 2nd page of entries I'm redirected to the home page:
http://luigisettembrini.gov.it/page/2/?s=informazioni

2nd page for category posts work fine, so it's really strange:
http://luigisettembrini.gov.it/category/comunicazioni/page/2/