Every time I 'merge' my Calendar (iMac & iCloud server) it's whacked

Every time I merge my iMac's Calendar with the iCloud server's Calendar it totally whacks my iMac's Calendar.

Not only does it end up deleting most of my important events... it adds old events that I haven't seen in over a year.

What's happening.

Fortunately I have numerous up-to-date identical bootable duplicate backups (not Time Machine backups... which I don't use)... so I'm able to recover.

I'd like to be able to use iCloud so I can sync it with my iPod Touch 5G (which I have not even tried to do yet), since iCloud won't even let my original Calendar events alone without completely whacking them.

EDIT: I have never been able to get the merge to ever complete either... the progress bar just keeps spinning.

Thanks for any advice.

Ron