Restart - BlogsMU Theme signup form - Blog URL suffix text incorrect for subdomain install

David asked me to restart this thread. Old thread was here:
https://premium.wpmudev.org/forums/topic/blogsmu-theme-signup-form-blog-url-suffix-text-incorrect-for-subdomain-install

Note: Old thread had some important information including link to related BuddyPress bug (that would need fixing in BlogsMU theme as well).

The problem I'm having is with the signup form at the URL /register

Under Blog Details when the user checks the box "Yes, I'd like to create a new blog" there is an input box under "Blog URL (required)". For a subdomain install, the suffix text is incorrect.

What I expect to see here is http://( ).mydomain.com

What I see instead is http://( ).www.mydomain.com

I tracked this down to
wp-content/themes/blogs-mu/registration/register.php:
.<?php echo str_replace( 'http://', '', site_url() ) ?>

I was able to fix it with:
.<?php echo str_replace( 'http://', '', get_site_url(1) ) ?>
where the argument value "1" is the blog id of my root domain (i.e. mydomain.com).

Is this a known bug?

Thanks,

Scott