Issues with variable substitution on action URLs

[nickpl]

I'm not sure if I'm trying to use $active_user wrong, but here's what I have in my config file:

Code:

action_url.registered = http://sipserver/test.php?ext=$active_user&ip=$ip
action_url.on_hook = http://sipserver/test.php?ext=$active_user&ip=$ip
action_url.call_terminated = http://sipserver/test.php?ext=$active_user&ip=$ip
action_url.idle_to_busy = http://sipserver/test.php?ext=$active_user&ip=$ip
action_url.busy_to_idle = http://sipserver/test.php?ext=$active_user&ip=$ip
action_url.setup_autop_finish = http://sipserver/test.php?ext=$active_user&ip=$ip

What I want is for the phone to substitute $active_user with the extension number, so for example if I'm in extension 24 I want these actions to get the URL "http://sipserver/test.php?ext=24&ip=10.10.95.201"

I've found that sometimes $active_user is replaced with nothing instead of the extension number, but the $ip substitution is always correctly replaced with the IP address of the phone:

action_url.registered: $active_user and $ip work
action_url.on_hook: only $ip works
action_url.call_terminated = $active_user and $ip work
action_url.idle_to_busy = $active_user and $ip work
action_url.busy_to_idle = only $ip works
action_url.setup_autop_finish = only $ip works

Is this a bug or is there a more correct way that I should be getting the extension number? I'm testing on a T46G running 28.83.0.57.

Thank you!