Theoretically this error should not occur but for some reason should be a duplicate value present the UI would no longer be usable for that field.
Steps to reproduce:
1. Add a duplicate value for a multivalue field in the database and recreate the admin-ui index (e.g. the contributor field)
2. Open the series/event details dialog
The values aren't displayed.
Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: value in params.value, Duplicate key: string:XY, Duplicate value: XY
The values are displayed.