right link wrong page displayed

Hi,something weird happens in my blog.
I have a sidebar with both links to pages and links to specific categories I created to display different topics. http://www.goethezentrumtriest.it/ is the website.
So, it happens randomly that I click on a label on the left (i.e. Biblioteca) and it fails to load the corresponding url…and it displays the page that can be reached when clicking I PROGETTI.
Other times (most of them )it works perfectly. BTW anytime it fails, indipendently from the label clicked, the page displayed is always the Progetti one.
Any clues?
Thank you