Having admin on different host breaks attached images

you can configure the tinymce to use relative paths for images using the tiny_mce_before_init like this:

function tinymce_relative_path( $init ) {
 $init['relative_urls'] = true;
 $init['document_base_url'] = 'http://www.mysite.com';
 return $init;
}
add_filter('tiny_mce_before_init', 'tinymce_relative_path');