I need WebSphere Portal to clear Render Parameters on page change. What's happening now -and it's a Navigational State feature of the product- is that the render parameters that I used in some URL's are being encoded in the URL, so even after I leave the page when I return my render parameters are still there.
You can try some of the options from the link below if you're allowed to create friendly urls or modify the theme navigation to use keepNavigationalState attribute.
http://www-01.ibm.com/support/docview.wss?uid=swg21586973
Edit: I looked up the portlet code where I thought I removed parameters from a RenderRequest. I actually was using the PortletSession to move an attribute from a processAction method to the doView. I then removed attribute from the session so it wouldn't be used on a page refresh. It's kind of a hack and you will need to turn on public session to support anonymous users ( http://publib.boulder.ibm.com/infocenter/wpdoc/v6r0/index.jsp?topic=/com.ibm.wp.exp.doc/wps/srvcfgref.html - Go to Navigator Service) but it's another option to think about.