I was looking into the issue you are describing and have found a great resource for troubleshooting an iCloud acccount setup in the Calendars application.
Its named iCloud: Troubleshooting iCloud Calendar and can be found here: http://support.apple.com/kb/TS3999
I recommend using the section called Troubleshooting Calendar on OS X Moutnail Lion (iCal on OS X Lion):
Note: For instructions on setting up iCloud Calendar with Calendar or iCal on your Mac, see iCloud Setup.
If you are having trouble with Calendar or iCal on a Mac and you are using iCloud Calendar, try each of these steps, testing after each to see if the issue is resolved:
- Make sure you are using OS X Lion v10.7.2 or later. Click here for help verifying the version of OS X you are using.
- Make sure your computer is online. Attempt to view www.apple.com and iCloud.com. If you can't connect to the Internet, your iCloud calendars and events will not update in iCal. Click here for more information about troubleshooting your Internet connection.
- Verify that your iCloud member name is entered into the iCloud Preference pane in System Preferences. See iCloud Setup for more information about setting up iCloud on a Mac.
- Make sure you enter and update calendar information in the iCloud section of Calendar or iCal. Only calendars and events in the iCloud section of the Calendar or iCal Calendar list will be pushed to iCloud. Both Calendar and iCal for the Mac support the display of and interaction with multiple accounts and datastores, for example, iCloud, On My Mac, Exchange, Google, and so on. This makes it easy to create or modify events or calendars in a section of Calendar or iCal that may not be updating iCloud. Learn more about moving local calendars to iCloud.
- In some cases, you may find that you have data duplicated in both the local On My Mac and the iCloud sections of Calendar or iCal. Learn more about resolving this issue.
- You can make the iCloud calendar your default calendar for all new events. In Calendar on OS X Mountain Lion, choose Calendar > Preferences > General, or in OS X Lion, choose iCal > Preferences > Generaland under the Default Calendar heading, select one of the Calendars under the iCloud heading. Close the Preferences window to save this change.
There is more information in that section to troubleshoot than in this snippet.