Using phpMyAdmin, I can change the post_type from a page to a post.
From the WordPress admin area, this seems to work fine. The page is now in the Posts area and I can add tags and such. In fact, I republish the post and it posts fine to my front page as the most recent post.
But the single post permalink just sends me to my 404 page.
If I change my permalink, say, from my-post-title to mypost-title, that works fine.
But I have several existing pages which I want to change to posts and keep at the exact same URLs.
I've tried just copying the content, deleting the page and then creating a new post, but that just creates the same problem. The new single post URL -- if identical to the old, deleted page URL -- still sends me to my 404 page.
So what additional step do I need to take to clear the old permalink association in the database?
I'd prefer to not do a 301 redirect or anything.