License Manager – Reappearing Users

Every few weeks, Event Viewer on my Primary Domain Controller complains that I’m out of NT licenses.

I go into Admin Tools -> License Manager, double-click Windows NT product, and then select and revoke Users that haven’t logged into NT in over ayear. Once done, I am within the number of purchased licenses.

However, after a few more weeks, I get the same message about being out of licenses and the users that I had revoked last time are back again. Why?