Currently if you try to generate a cross siteaccess link the path of the target siteaccess isn't cut off from the generated Url.
This is caused because rootLocationId in here https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/Core/MVC/Symfony/Routing/Generator/UrlAliasGenerator.php#L109 is set to the current siteaccess's locationId.
Therefore the wrong path prefix is generated.
Somehow rootLocationId in this context should be set for the specified target siteaccess and not used from here https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Bundle/EzPublishCoreBundle/EventListener/RoutingListener.php#L57
See my dirty hack (don't fix it this way): https://gist.github.com/bennyklotz/85747cd3b08ab963580e