Sort of, it’s a custom page template that is part of the Copyblogger theme from Chris Pearson. I looked at the source, but couldn’t see anything that would indicate a specific url.
I also thought it was interesting that it did not use my custom 404 page template and used the default error page from my web host. If you go to http://captainpenguin.com/free-candy, or any other faulty url for that matter, you get the 404 page built into the theme.
No, the only thing in my .htaccess file is the stuff for Wp-SuperCache. And yes, there is a page called “Sitemap”, and the template is set to “Sitemap”, and as I said before, it worked until I changed the slug.
i don’t have any more suggestions from my own experiences, sorry.
Have you cleared out supercache? Does it have a copy of the page cached with the old URL?
SOMETHING is overriding the term “sitemap” which is why you are getting the Apache 404 and not the WP 404. That is your clue. You have to think through what you have done, how you have things set up, and what would be affecting the term sitemap? Running a Google Sitemap plugin by any chance?
What I was getting at earlier is if you are using the Google Sitemap plugin, its possible it is internally using the link to the permalink sitemap, even if you have no page of that name. Thus it could be that two sources are trying to use the same permalink. Try changing the permalink of your internal sitemap to something else and see if that clears the problem.