When a work is initially created with a duplicated attribute, both duplicates are kept. See e.g. edit #79082724 (contrived example) or edit #73655126 (real example).

This is a bit inconsistent with the other edit types.

• On merges, a work with duplicated attrs will have them deduplicated, regardless of the direction (1, 2, 3; 1, 2, 3)
• On edits, turning two different values into the same one will have them deduplicated (1)
• Also on edits, adding a duplicate value will not add a duplicate (1, MBS-11606 related)

They should also be merged when the initial Add Work edit has duplicates.