I'm stumped and need help.
My slave site template for urls looks like this.
www.{site_url}/multisites/{site_id}
http://{site_url}/multisites/{site_id}

However, when a client of mine creates a slave from the front end the urls end up looking like this.
http://www.www.mysite.com/multisites/123
http://www.mysite.com/multisites/123

I can not duplicate this issue when I create a slave site from the front end UNLESS I log in as his user. When I create a slave site from the front end the urls are normal and look like they should.

Can you explain why being logged in as his user would cause multisites to prepend and extra www on to the url?

joomla 2.5.4
Multisites version 1.2.87

I've attached a screenshot for you.

The {site_url} contain the current site URL.
This means that if your customer go on the "www.domain.com" the {site_url} is "www.domain.com".
If the person connected the url "domain.com" the {site_url} is "domain.com" (without the WWW).

As your rule specified that you want the current site URL and its variant with WWW in front of it, this is normal that you have double www.

As you propose a website creation from the front-end, it would be better to hardcode the value of the domain rather than to use the current URL value that you do not necessary control.

JMS perform an exact matching and does not add or remove value to any fields.
This also mean that it is case sensitive. In the case of website creation from the front-end, it is better that you hardcode the domain name to avoid that users enter variant that you would not control.

Thank you. I understand.