Why does iCal delete the details of a new event?

Running OS X 10.9.5 with a 3.06 GHz Intel Core 2 Duo and 4 GB 1067 MHz DDR3 (yea, I know it is old). After our last OS X upgrade, iCal is now deleting all the details of new and copied events. I input the data into an event and a few seconds later iCal resets the event to 0900 with the generic title "New Event" and tags it to my wife's calendar. All details are lost. The work around is to remember to open an event and change the calendar tag immediately, wait a few seconds for the reset, change the calendar tag again, wait a few seconds and then add any details like time, length of appointment, notes. I see lots of community discussion on this same topic, but I haven't seen any solutions. I'm afraid to upgrade to the next OS X because iCal may not longer be an isolated problem. I'd hate for Mail, Contacts and any other application to go kaput like iCal!!!!