The reporting manager drop-down (Edit/create requester screen) duplicates names in the list when that manager has multiple email addresses.
My expectation would be that there would be only one item in the list per user.
Here's the manager:
Here's the reporting manager field for another employee:
An alternative, but less desirable solution would be to list the user name and email address in the dropdown. So the above would be listed as "Tori Parker (firstname.lastname@example.org)" and "Tori Parker (email@example.com)"
As far as I know, selecting either option results in the same data in the user record