Logging from outside CI

[eluser]jalalski[/eluser]
I have a callback page that is called from outside the site, yet I need to make use of CI facilities.
So, I'm loading the Common, Config, Language and Log classes and instantiating the basic system, but calls to log_message are silently failing to write anything.
Simlarly:

Code:

$LOG =& load_class("Log");
$LOG->write_message(...)

doesn't have any effect.

Any clues?