Microsoft Forefront Threat Management Gateway (TMG) 2010 Service Pack 2 (SP2) introduced the account lockout prevention feature. If you use this feature, you see a message when an account is locked in Forefront TMG 2010. However, after you install Rollup 4 for Forefront TMG SP2, you notice that you no longer see the message. This problem occurs only if the credential validation method is set to Windows. If you use LDAP verification, alerts are logged as expected.
This problem occurs because of incorrect logging logic that was introduced in Rollup 4.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.