bug in old permalinks

I think I’ve found a bug in permalinks.
Version: 2.8.2
htaccess:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

permalinks setting in settings:
/%postname%/

And finally, description of the problem:
I have the following site structure:
site.com – my main wp install folder
site.com
—folder
——new_folder
———folder1
———folder2

So I had a page named folder2 in wordpress, and it created a permalink for it. Then I rename the post to be a child of a another page, and of course the permalink was changed in page editing mode to mirror that. For example, PageParent/Page_child

But when I try to open site.com/new_folder/folder2, it gives me 404. When I name my Page_child page to be named again folder2, and access the site.com/new_folder/folder2 path, it opens instead site.com/PageParent/Page_child?

That is really weird… really 🙂