Importing vCards to iCloud from Address Book vCard Backups.
It seems that your vCard version setting must be set at 3.0 or higher for iCloud to properly import your contacts from Address Book.
Otherwise, your iCloud contacts will get erased if this version setting is set to 2.1 within Address Book.
Address Book and iCloud Contacts-OTHER, Mac OS X (10.7.4), vCard version settings 3.0 vs 2.1