Yes, Joe, I did use the Cocktail Uninstaller.
FWIW: all is dandy on my MacBook Pro and on my wife's 22" iMac. It is only on my 27" iMac that this issue is present.
I wonder (guess) if the problem is with Notifications and not with Cocktail. If it were in Notifications, where do you suppose it might be? Indeed I am perplexed. It seems to me there should be a file listing all the apps/files in Notifications. If so, might this be editable?