XSI:NIL Unary Tag

In IS8 I have an instance where I need to send a unary null tag from a document in IS, which is to be received via the soap xml like so:
(e.g. Schema Tutorial)

The use case is a required document has strings, but the document itself is required. The webservice needs to know if this document is null.

For some reason, IS is generating tags as such in SOAP:

documentToXMLString however creates . If you create an xml node and manually create a soap message from the xml string, when the soap message is generated it oddly converts it back to the binary tag again.

Should this be a unary tag and if so is that a (minor) bug?