User must change password at next logon - Windows 2003 AD issue

The "User must change password at next logon" box is no longer available to
our help desk. Delegation is set up to allow them to change the password
and until a couple of days ago they were able to change a user's password
and check the "user must change password at next logon" box. Now although
they can still change user passwords the box is not available to them as it
is grayed out. This happens whether they right click on the user account
and select reset password or right click on the user account, click
properties and select the account tab.

Has anyone else had this problem? Please help.