Users logged in without authentication

I got the following warning in the logs for an apparently successful LDAP login:

warning: Unknown modifier '.' in C:\apachefriends\xampp\htdocs\drupal4\modules\ldap_integration.module on line 310.

My settings were as follows:

Port:  389
DN: CN=users,DC=mycompanyname,DC=com
Filter:  (&(objectClass=user)(sAMAccountName=%s))
Login pattern:  /(\S+)@(\S+)\.(\S+)/i.
Login replacement:  uid=$1

I picked up the extra period at the end of the login pattern by cutting and pasting from the text next to that line on the form. (I was trying out different combinations of LDAP settings, all of which failed with the usual "unable to bind to server: invalid credentials".) At first I was excited that LDAP was working, but then I saw the log warning and started having doubts.

It seems that the warning/error is letting my login pass through to Drupal as if it had been approved, but my credentials aren't actually going to the server at all. I tried a fake user at a fake domain and it was allowed on as well.

I'm using a XAMPP install (Apache 2.0.52, PHP 4.3.10) on Windows XP. The LDAP DLL is definitely loading and working.