Base href picking up wrong domain

I’ve got a dedicated server at Rackspace with multiple clients managed by plesk

I’ve noticed on two occasions that <base href="[[++site_url]]" /> is picking up the default domain for the server rather than the domain for the specific client, which results in a page mixing elements from the clients site and the default site (which embarrassingly is mine).

I’ve asked Rackspace if there’s any corruption between domains and they say it’s all clean.

If I replace [[++site_url]] with "www.actualdomain.com" it all works fine.

I’m wondering how it’s possible for [[++site_url]] to get the wrong address - is it being generated dynamically for every page via the .htaccess and occasionally it’s picking the default www based on the servers ip?

First of all, if your website is accessible from multiple host names, I recommend always using the non-cacheable syntax with this tag, e.g.

Second, you can always force the value by setting the site_url as an explicit Context (or System) Setting.

Thanks