As a bit of sensible site management I recently moved a group of stand-alone WP installs into a single WP multisite instance. WP multisite allows you to serve multiple domains from a single WordPress install, which makes system management much easier. It also makes plugin management exponentially more difficult, but that’s for another day.
I setup a temporary site to do the install and plugin/theme testing, and then once the content was imported I tried to update the WP multisite settings to take over from the previous domain. I went into the Site’s settings, and updated the values for Siteurl and Home.
And it worked, sort of. WP served the right content… but at the wrong domain.
Site Address (URL) =/= Siteurl
Turns out setting new values for the Siteurl and the Home url are only two of the things you need to do.
You also need to update the value for the Site Address (URL). You may have thought that Siteurl and Site Address (URL) are the same things, but you would be wrong.