Google Calendar is updating its own contents (events data) via AJAX only when user is making manual changes -- i.e. adding, removing or updating events. If it remains open, but unused, it will not update its contents itself periodically. This may lead you to at least confusion, if not a fuckup.
If you leave it open on your computer (on one of your browsers tabs) for a longer period of time (for example you suspend your office computer while going home on weekend), you will not see any changes you did from other sources (from a mobile device, home computer etc.) once you're back. Calendar will remain as it would be untouched for the entire period of time.
If you force it to refresh itself, by pressing F5 in a browser, it will keep loading some strange, outdated, temporal events dataset from the time you left it. In other words, you can refresh Calendar page as many times as you won't and it will keep claiming that nothing has changed since you left it.
You have to log to the Calendar from that other source (from which you made all the changes) and force Calendar synchronisation and only then refresh your current, stuck Calendar to see all the changes. Strange and stupid.