Mail addresses not filled in

I'm sending email using the POST /Mail  (createMail) endpoint.

I'm only filling out mail addresses

{
     "attachments": [{
               "name": "Quote.pdf",
               "id": "73e90730-cdcd-11e7-bfae-02e359029409",
               "type": "upload"
          }
     ],
     "related": {
          "id": "bea98ad2-c2cf-11e7-a51c-02e359029409",
          "type": "Quotes"
     },
     "subject": "Test voor klant",
     "html_body": "<p>Hier is de body<\/p>",
     "cc_addresses": [],
     "to_addresses": [{
               "email": "brecht@mydomain.com"
          }
     ],
     "bcc_addresses": [],
     "email_config": "167ce952-b8b2-11e7-a85f-063b661e1dc5",
     "status": "ready"
}

The email in Sugar does not display these address, even if I do receive the email

I think this behavior only started showing since 7.10.

I have tried filling out the names of the email address objects, but to no avail.

How do I get Sugar to display the email addresses?