EmberJS : JSON-API Errors for one field are included in other field's errors

I have a ticket model with only a subject and content field.

subject: DS.attr('string'),
content: DS.attr('string')

On a new wiew, submitting a new ticket with content but without a subject return the following error :

{"errors":[{"source":{"pointer":"/data/attributes/subject"},"detail":"doit être rempli(e)"}]}`

Here is the controller action :

saveTicket(ticket){
      let promise=ticket.save();
      promise.then(
        () => this.transitionToRoute('tickets')
      );
      return promise;
    }

ticket.errors.subject[0].subject correctly contain the detail from the server's answer, however, ticket.errors.subject[0].message also contain the error message.

Why is the error attached to every field ?