I use TWO iCloud accounts to share addresses (contacts) with a second person (iCloud account).
Since I have this set up, 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.
I am sure is it (another) bug! Not fixed in 10.8.3.
Is there hope for 10.8.4?
MacBook Pro (15-inch Mid 2009), OS X Mountain Lion (10.8.2), 4 GB RAM