WordPress address (URI) problem

You mean the URL changed all by itself???

This is what happens if your site is available at https://www.mydomain.com AND https://mydomain.com – Somebody typed the second address, WordPress thought it was a server change and updates its configuration. Very bad. Imagine someone typing the IP adress as well.
To avoid this, you can comment out these lines in wp-login.php:
// If someone has moved WordPress let's try to detect it
if ( dirname('https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI']) != get_settings('siteurl') )
update_option('siteurl', dirname('https://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI']) );
@wp developers: please remove this “smartness”, I think this causes more trouble than it helps…

thanks very much~~~~~~~~~~~~~~~
you do me a great favor!

Also see this thread.

Amen to that. It’s screwed up my site in even more bizarre ways, bringing up old domains I haven’t used for months. This is a prime example of why cleverness is not a good thing.