DST option reverts

I was having a problem where a user would input an
appointment into their calendar for the proper time, but
it would show up later an hour off. I knew this was a
Daylight Savings time setting, so I went in through the
computer clock in the system tray and checked it. It was
originally checked. How it got unchecked, I don't know.
Any way. When I went into
Outlook>>>Tools>>>Options>>>Calendar Options>>>Time Zone
and checked that setting, the "Adjust for Daylight Saving
Time" checkbox was not checked, and the "Current Time"
box showed EST, 1 hour earlier than the actual time. I
checked the DST box, which caused the proper time to be
shown in the "Current Time" box, OKed out, then went in
to check and make sure the setting had taken, and noticed
it hadn't. The "Adjust for Daylight Savings Time" box was
unselected and the "Current Time" box showed the
incorrect time (EST).Can anyone explain this behavior and
how to correct it?