Change url since the last update

I just upgraded to the latest version is I again the url problem now as you can see in the url I forums and not forum

How do I correct the problem before you index my new url and create me duplicates?

I had already spoken here: http://stackideas.com/forums/url-problem-after-upgrading-to-version-4
and I have solved the problem, but do not know how, if it me if I fix it occurs again on its own, thanks a lot

stefano