When using the Rally web services API (WSAPI) to update an object, the payload contains the updated value, however, there is an object in the response body that does not show the field being updated.
This can be caused when there is an error reported by the API. All API transactions are treated as atomic transactions and if there is a validation error, then the entire transaction is aborted and an error reported.
The response body will differ depending on whether the validation is failing on an internal field versus a custom field. A custom field may show a response body of the target object and this should not be taken as an indication of update success.
Resolve the offending validation error reported in the error object in the JSON response and retry the request.