When an admin deactivates a user then presses the "Update User" button after, the user appears to be deactivated but was actually reactivated due to the press of the Update User button. Pressing the Deactivate icon is the only step needed.
Press the Deactivate icon:
Do not press the "Update User":
We are working to disable this button to prevent the confusion and error of reactivation, but until we deploy that change, this is the correct method to deactivate a user.