Describe the bug

When adding a contributor or subject field by "duplicate button", an existing contributor is deleted and another is duplicated.

To Reproduce
exemple https://bib.rero.ch/professional/records/documents/edit/2076666 :
I want to add a new contributor between Martin, T. J and Chinn, Simon,I click on duplicate icon beside agent Martin, T.J. to add it..
Then one contributor (Chinn Simon) is deleted and another (Chinn Jonathan) is duplicated.

Expected behavior

the new field is simply added

• server: [bib.rero.ch] [bib..test.rero.ch]

• browser: Firefox

Screenshots

before adding field:

after field is added: