we have our mantis installation running on an internal webserver, which can be accessed from the outside through a different webserver (apache which uses ProxyPass). In that case, the $g_path contains the wrong hostname. Its set to the internal name of the webserver, not the one the user specified in the browser.

This leads to all the icons not being loaded.

I added this to config_defaults_inc.php:
if ( isset( $_SERVER['HTTP_X_FORWARDED_HOST'] ) ) {
$t_host = $_SERVER['HTTP_X_FORWARDED_HOST'];
} else if ( isset( $_SERVER['HTTP_HOST'] ) ) {