Known issue. From the xda forum:
'The problem is not that it won't sync with google calendars - it does. The annoying issue is that when you make a new calendar entry it defaults to 'My Calendar' rather than the google one. You are given the option to choose the google calendar but it is such a pain having to do that for every entry when with all other calendars you can choose your default calendar.'
Go with Business Calendar or GooCalendar - they sync without a problem.