Problems with my iCal and mail attachments on Lion

I just switched to Lion and have been having problems ever since with my iCal. I switched from Mobile Me to iCloud. However, the calendars are all synching except for one thing - any invites that come to me as mail attachments and I add to my calendar, only add to the local machine. They don't synch to iCloud and therefore do not synch to my other devices. i.e. My iPad, my MacBook and my other iMac.

Any thoughts or suggestions would be greatly appreciated!!!