Three identical e-mail notices for one checkout

Steps to reproduce

1. Go to Checkout, and check out an item to a patron
2. Call patron-action-session-storage/patron-action-sessions to verify that a checkout session is ongoing for that patron
3. Wait for the checkout session to close (in the Chalmers env it's set to 2 mintues)
4. Call patron-action-session-storage/patron-action-sessions to verify that the above checkout session no longer exists
5. Check the inbox of the patron to verify that a checkout receipt for the session has been sent

Expected result

There is a new e-mail containing a checkout receipt for the checkout session.

Actual result

There are three new e-mails each containing an identical checkout receipt for the checkout session.

Other comments

There is only one checkout-by-barcode request registered during the checkout session, so I am pretty sure that I have not accidentally "checked out the item twice" during the same session. There are, however, three individual POST requests - with different id values - to end-patron-action-session.

"postData": {
            "mimeType": "application/json",
            "params": [],
            "text": "{\"actionType\":\"Check-out\",\"patronId\":\"8611bc8e-c1a9-4227-8573-887007040c1a\",\"id\":\"dafcf607-ca11-48d5-a57b-84d79a3a44ca\"}"
          }

 "postData": {
            "mimeType": "application/json",
            "params": [],
            "text": "{\"actionType\":\"Check-out\",\"patronId\":\"8611bc8e-c1a9-4227-8573-887007040c1a\",\"id\":\"2e48dcfa-117f-4f6a-867c-55a0c8276d21\"}"
          }

"postData": {
            "mimeType": "application/json",
            "params": [],
            "text": "{\"actionType\":\"Check-out\",\"patronId\":\"8611bc8e-c1a9-4227-8573-887007040c1a\",\"id\":\"55697d0a-e150-4c16-a2a8-f66c44e776a0\"}"
          }

When I tried checking out the item again and ending the checkout session manually using the UI button, I only received one e-mail (and could see only one POST request to end-patron-action-session).