Add post overwriting permalink from previous post in 4.6

It seems to be a caching issue, though there isn’t a single cause for it. There is still ongoing discussion, as well as multiple suggestions for fixes about this on the WordPress issue tracker:

https://core.trac.wordpress.org/ticket/37889

You can fix the symptoms by ensuring pages under “/wp-admin” are never cached. If using Apache, you can do this by adding the following to your Apache configuration:

<LocationMatch "/wp-admin">
    FileETag None
    <ifModule mod_headers.c>
        Header unset ETag
        Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate"
        Header set Pragma "no-cache"
        Header set Expires "Wed, 11 Jan 1984 05:00:00 GMT"
    </ifModule>
</LocationMatch>

You should place this after any other Header directive in your Apache configuration. If ensure you can put this in either:

• .htaccess on your project root;
• The <VirtualHost> section of your main Apache configuration (assuming you’re using virtual hosts!)

And then check in a web browsers these headers come as expected.

For a solution fixing the issue (rather than just the symptoms) keep following the bug report above.