Outlook 2003 permissions change

We set all of our calendar permissions to reviewer and in the last month some
calendars reverted back to access being none. I am not sure why this would
happen is it some of these updates that have been released recently? or
maybe the tzmove tool that was run on all the mailboxes to update DST? I am
not sure what would change these permissions without actually physically
going in and changing them.
Any suggestions?