duplicated addresses in mail-to autocomplete of Mail.app

I use TWO different iCloud accounts to share addresses (contacts) with a second person.

Since I do that, the autocomplete of Mail.app lists Email addresses that are in "shared/linked contact cards" twice.

In addition, the arrow-down function to select one of the several Email addresses that Mail.app offers after typing a few letters of the name does not work any more. It is not possible to "move" over the duplicated preselection entries.

Am I the only person who has this problem?

Can it be fixed by the user (me), or is it a bug?