Menacing clocks showing up

I am using outlook 2003SP1 and having an issue where my
calender will change itself...I can make a normal meeting
or appointment or whatever and close it and reopen it
sometime later and some of these appointments now have
changed to more then day and added a small black clock
beside it and change the time from like 1:00am to 1:00am
the next day....You can reset it back by clicking "All Day
Event" off and on again, but the time is still messed
up...The strange thing is----this only happens to some
appointments during a few weeks or months then it stops
for a period of time, then does it again. We can't find
anything that could be triggering it...Any ideas?