Yeah, that's a tough one. It goes against Portal paradigms. Portlets keep their state even as you navigate away from them, and that's how Portal is designed.
By the way, if you're using RAD 6 with WebSphere Portal, you might as well use the JSF libraries that come with RAD 6 for Portal. They are quite good, though a little buggy sometimes. The tooling works rather well too. Plus, they are integrated much better than the Sun RI with RAD 6 and Portal, and if you have issues, you can always call Tech Support
