Off site links not working

Greetings.

I've been using Fieldset Menus on my site without any issues, until I try to create links that are off-site. When I attempt to create a new link that leads off of my site, the offsite link has my site's address appended to the first part of the link. For instance, I create a link to http://www.slashdot.com. When the link is clicked on, the link redirects to http://www.mysite.com/http://www.slashdot.com. Any idea what's going on?