cameuh on "[Plugin: WordPress MU Domain Mapping] Domain Mapping breaks some xmlrpc functions"

I try to use Live Writer on a multisite wordpress blog which is mapped to a primary domain. Live Writer cannot add the blog.

I've found where is the issue in the code but I don't understand why.

Here're my blog details for the purpose of the explanation:

Network is "at.cameuh.net"
Site is "easytrading.at.cameuh.net"
Primary Mapping for the blog is "easytrading.eu"

When setting up my easytrading.eu blog in Windows Live Writer, this XMLRPC request returns an empty array response:

* LW request:

Host: <strong>easytrading.eu</strong>
<methodCall> <methodName><strong>blogger.getUsersBlogs</strong></methodName><params>
<param><value><string>0123456789ABCDEF</string></value></param>
<param><value><string>cameuh</string></value></param>
<param><value><string>shutitup</string></value></param>
</params></methodCall>

* WP executes this PHP code to SELF-QUERY using XMLRPC to convert blogger API to wp API:

wp-includes/class-wp-xmlrpc-server.php

function _multisite_getUsersBlogs($args) {
    global $current_blog;
    <strong>$domain = $current_blog->domain;</strong>
    $path = $current_blog->path . 'xmlrpc.php';
    $protocol = is_ssl() ? 'https' : 'http';

    $rpc = new <strong>IXR_Client("$protocol://{$domain}{$path}");</strong>
    $rpc->query('<strong>wp.getUsersBlogs</strong>', $args[1], $args[2]);
    $blogs = $rpc->getResponse();

    if ( isset($blogs['faultCode']) )
        return new IXR_Error($blogs['faultCode'], $blogs['faultString']);

    if ( $_SERVER['HTTP_HOST'] == $domain && $_SERVER['REQUEST_URI'] == $path ) {
        return $blogs;
    } else {
        foreach ( (array) $blogs as $blog ) {
            if ( strpos($blog['url'], $_SERVER['HTTP_HOST']) )
                return array($blog);
        }
        <strong>return array();</strong>
    }
}

* Here's this request received by Apache:

Host: easytrading.at.cameuh.net
<?xml version="1.0"?>
<methodCall><methodName>wp.getUsersBlogs</methodName>
<params><param><value><string>cameuh</string></value></param>
<param><value><string>shutitup</string></value></param>
</params></methodCall>

* This call returns results using easytrading.at.cameuh.net!

* The problem here lies where WP Self Query uses $current_blog->domain to setup the URL.

* Could you fix the plugin so the proper HOST (easytrading.eu but not easytrading.at.cameuh.net) is used when WP tries to self query?

* I've workarounded this issue by statically setting $domain='easytrading.eu' -- that works while only this blog is remotely used.

http://wordpress.org/plugins/wordpress-mu-domain-mapping/