The "Assign" button doesn't turn off if you click on it. This happens only in
menu "Option"; Tab "Security" in Outlook Express. Windows Mail in Windows
Vista. is also affected with the same issue.

Reproducable steps:

Goto Outlook Express
Goto Menu "Tools"
Choose "Options"
Choose tab "Security"
If you click on the "Assign" button the active button "Assign" doesn't go to
inactive (light gray).