I've been having a problem with my Google calendar and it's updates "sticking" in that I'd do an update via the phone or the computer and within an hour, it would disappear. It was like something would have an earlier modified date and overwriting any changes.
I realized that I had downloaded and installed Google Calendar Sync and synced my Outlook calendar with my Google calendar with a "2 way" sync as recommended. It seems that it kept taking the Outlook version and considering it a newer version and replacing the Google calendar. Once I uninstalled it, reinstalled it and selected "1 way - syncing Google calender to Outlook calendar" my issues have so far gone away. This worked fine for me as I haven't used the Outlook calendar to do any updating at all.
I know some people have issues with their calendar so maybe Outlook (Google Sync) can be the issue.