You try to add a user. To do this, you type <Myalias>, and then you click the Check Names button.
In this scenario, <Myalias> is resolved despite the filter. The expected result is that the Check Names button honors the LDAP filter. However, the LDAP filter is not honored when you click the Check Names button.
To resolve this problem, apply the hotfix that is mentioned in the following Microsoft Knowledge Base article:
957691 Description of the Windows SharePoint Services 3.0 hotfix package (Sts.msp): October 28, 2008
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.