Workaround:
Always create events with the "quick event creator" or whatever it's called, it's the + sign at the top left corner of iCal. This lets you enter the event name, date and time and THEN sends it to the Calendar, and using this technique I never again had this frustrating problem. I sync with Exchange Server AND iCloud, so this was crucial.
It seems to me that when you open a new event by clicking on the calendar, iCal quicky sends it to the cloud even before you are done typing what it is and such, and this creates coordination problems. When you do it "off calendar" and send it already created, it doesn't have the time to send multiple versions of the same event to the cloud and the problem doesn't occur.
I have been a SUPER loyal Apple user. But I am almost to the point of succumbing to the PC world. I am a business user, and in my world I need to be able to see my peers' Exchange calendars, their contacts, I need reliable calendars, I need to access Excel plugins that never work on the Mac versions, and so on and so forth. By coming out with shoddy products such as this version of iCal, Apple isn't helping my loyalty.
Any way, I hope this helps someone else.