Two identical iCloud Group lists in Contacts

For some reason - & this has been the case for as long as I remember, years at least - I have two sets of iCloud Contacts in my Contacts address book.

One is called 'iCloud (me.com) the other just 'iCloud'

The content of each is identical, except for one thing, & I'm a bit scared to test this too hard for fear of breaking something...
If I delete a contact group from either list, it deletes it from both after showing the sync 'wheel' for a couple of seconds.

The difference is…
If I do this from 'iCloud' then Cmd ⌘ Z to undo, it restores the group to both lists within seconds.
If I delete from 'iCloud (me.com)' then undo, the group is not restored to the 'iCloud' list

Has anyone any clue as to why this may be & if it is truly safe to delete one list entirely?

Sorry for all the blurriness ;-) The highlighted group is the one I just deleted then undid, which didn't return it to the duplicate group. The actual contacts, btw are still preserved in both lists, even though the group has now gone.

Incidentally - my iPhone shows only one list… & appears to be a mirror of the 'iCloud' list [the bottom one in the picture, with one group now missing]

Found it!

I have no idea how it actually was set up, as I discovered a pref pane through another question on Ask Different which I'd never seen before…

System Prefs > Users & Groups >[unlock] > Right click user name > Advanced Options...

My [email protected] account was listed twice in aliases.

I deleted one - the duplicate iCloud account in Contacts disappeared.
So far I've seen no unwanted side-effects.