READ THIS ENTRY, NOT THE PREVIOUS ONE - SEEMS APPLE'S FAULTY SYSTEMS ARE DUPLICATING ENTRIES HERE TOO!!! :-P
The Apple Bug Reporter is for Apple Developers only.
To be clear, we are talking about a longstanding bug on Mac Desktop and Laptop computers running several versions of the OS, not iOS devices. Creating events on iOS devices actually circumvents the problem.
Since Mountain Lion, iCal has been named Calendar - and yes, the problem still exists today. I deleted iCal prefs (Yes, still so named - and no, there were no calendar prefs and yes, the iCal Pref regenerates when you relaunch Calendars) and the problem still exists and is 100% reproducible. Create a new event by double clicking on any FUTURE date. (when I create events in the past, this bug does not occur - I know, big help, but it might be a clue.) Name the event Anything. Wait a few moments to minutes (depending on lots of stuff) and presto! Your entry has been renamed the default "New Event". This time, when you go back and rename it Anything, it will stick. In my case, the bug is limited to events in shared calendars.
Note also that when sharing Calendar events, the reverted name "New Event" will be transmitted for that appointment / event. Not the correct name you initially created.
I also repaired permissions (two ways, twice) and after restarting and launching ONLY Calendar, the bug immediately reemerges.
A work-around I've found effective is to create the event in the default calendar and complete it. Click out of the event and then back into it to switch to the shared cal. Now it will stick on the first try.
Times have changed, Apple created this forum to share community info that would help other Apple suckers customers but now, it's time for Apple to weigh in on such grievous bugs and failings. At least comment on awareness by Apple Engineers, I would say that's the No.1 thing those of us who are dumb caring enough to share our experiences with other users would really, really, appreciate. Knowing we've been heard.
Do you hear us Apple?
And yes, this was submitted to https://www.apple.com/feedback/
Oh and look, after years of providing correct answers and salient feedback, I still have zero of those worthless precious points. They are SOOO meaningful.