OK well like I said, it's difficult to say what might be causing it without looking into the site closer. It's probably a cache setting somewhere. I'll get an option to turn the message off.
Don't delete the value in the regex filter - that value is there so that the page index is updated after you create/edit a tab. If you take it out, you'll have to restart your application every time you add, remove or modify a page.
For the 404 - umm, no - but it's just standard ASP.NET behaviour. I'll put it on my list of things to document and probably do a blog entry or something.