How can I update the description of the Customs Statistics Number using the REST API?

I would like to update the customs statistics numbers via the REST API.

I have used the following PATCH request:

URL: CustomsStatisticsNumberHandling.svc/CustomsStatisticsNumbers(CustomsStatNo='01022110')
Body: 

{"Description": "Hello World","CustomsUnitMeas": "F", "Cf_Companysite": "EC7E0EF2D979ED5DE0536379A10A1DB4","Cf_Importcode": "42"}

This request successfully updates the CustomsUnitMeas and the CustomFields. Only the description is not updated.

It is strange that in the HTTP response the correct value is displayed. In the database and in the GUI the old value is displayed.

Response:

{
    "@odata.context": ".../v1/CustomsStatisticsNumberHandling.svc/$metadata#CustomsStatisticsNumbers/$entity",
    "@odata.etag": "W/\"Vy8iQUFBVlk1QUFZQUFBKys3QUFCOjIwMjMwODI1MTUwNDU1Ig==\"",
    "luname": "CustomsStatisticsNumber",
    "keyref": "CUSTOMS_STAT_NO=01022110^",
    "Objstate": "Active",
    "Objgrants": null,
    "CustomsStatNo": "01022110",
    "CustomsUnitMeas": "F",
    "Description": "Hello World",
    "Cf_Companysite": "EC7E0EF2D979ED5DE0536379A10A1DB4",
    "Cf_Importcode": "42"
}

GUI: