Calendar syncing issues from MacBook on OS X

I am having issues with the syncing via iCloud of my Calendar, but only when making changes or creating new events on the MacBook (fine on iPad and iPhone).

The problem is as follows (using create event as example - same for changing exiting events):

Creating a new event, set time, perhaps the calendar it relates to (personal, work etc), set an alert, enter some notes.

As soon as I click Done, 'Updating' appears in the Calendar heading (syncing) and then ONLY ONE of the changes is saved. I then have to go in and change each of the other fields ONE AT A TIME, saving between each change and waiting for the Update to finish. It will not allow me to make multiplle changes to an event - new or existing.

I can do the same on my iPad or iPhone without a problem,

I am running OS X 10.8.5, Calendar 6.0 (1648). I do not want to upgrade the OS at this time.

I have searched through other questions to find a solution but have found nothing so far - happy to be pointed in the right direction.

Thank you!