If you set up a page parameter in pages.xml for a given page, go to that page, and the page is re-rendered due to an event, then page parameters disappear.
For example, if you add a button such as :
<h:commandButton value="Dummy" action="none"/>
Into either the search page, or the editcontact pages in the contact list example, then run the seam contact list example, anytime you click the button, the page refreshes, and the params disappear.
This kind of messes with the Restful URL ideas since having a bookmarkable URL will depend on whether or not there are event type buttons on the page, and whether the user has already clicked them.
Parameters are kept on the request URL when you use pageflows to handle the events, so if my page was in a pageflow that executed some action and transitioned on "none" to the same page that I was already on, the parameters would be present when I clicked the button and the page refreshed.