Winlogon always reverts the Userinit registry key

This is a cross post from microsoft.public.windowsxp.general. Sorry
for that, but not sure if that was the right place. Here it is.

We're trying to implement a custom userinit procedure in our network.

The user MUST register his/her time-entry within a custom application
(that we developed) just after the network authentication and before
the logon procedure continue.

Here's the sequence we're trying to achieve:

1. User authenticates in our domain providing his/her username and
password;
2. Gina calls Winlogon which in turn calls MYUSERINIT.EXE;
3. MYUSERINIT prompts for a time-entry;
4. User agrees clicking in a button;
5. MYUSERINIT calls the DEFAULT USERINIT.EXE and ends;
6. Logon continues.

The issue is that, everytime we manually change the HKEY_LOCAL_MACHINE
\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon using
REGEDIT.EXE the WINLOGON processes immediately revert it back to
USERINIT.EXE.

We confirmed this behavior through REGMON. There's an entry for REGDIT
changing the key and right after for WINLOGON reverting it back.

Is this a normal behavior?

We're using Windows XP Pro SP2.

Thanks in advance,

Yanko Hurta