SWORD module requires the X-Packaging header

The use of the X-Packaging HTTP header seems to be mandatory in the POST request, in order to create a new resource.
The SWORD Atom profile 1.3 says that this header SHOULD be used by the client, but is not mandatory. Its value must be one of the packaging formats accepted by DSpace. The specification also says that if the server cannot accept the format given in the header it MUST return a status code of 415 Unsupported Media Type.
However the actual implementation of SWORD acts in a different way. If the header is not present in the POST request, the server returns a status code of 500 Internal Server Error.
In the response there isn't any error message or stack trace.