Aparrently there have been changes to the Google Calender website. Events created here can now be assigned a colour. This has presumably changed the underlying file structure which may be what has upset certain phones!
Ok, last night I saw this for the first time.
My solution? I'm going to create a new calendar and move all of my events there.
It's actually quite simple to do.
In Google calendar, go to settings. There is a link under "My Calendars", after the list of all of the non-subscribed calendars, called "export calendars". This will create a zip file to save on your PC. If you unzip that file, you will see an .ics file for each of the calendars you have listed under "My Calendars".
Back to Google Calendar, Create a new calendar, give it a name. Now click on "import calendar", choose the .ics file that corresponds with your main Google calendar that you unzipped before, and import it into the new Google Calendar that you created. (You may have to refresh the Google Calendar page to see it in the list.)
Then, when you are sure that you have the events in that calendar all set, there is a "delete" link next to your primary calendar - you can click that to mass-delete all of the now duplicated events in your calendar.
You amy also want to go into the settings for that calendar to change notifications, etc.
Inelegant, but this works for me.