[Sipping-tispan] Reason header in Responses

Dear all,
Still the use of the Reason header confuses me.
With regard to the discussion of the retargeting draft the inclusion of a 486 in a 302 is discussed as possible.
But on the other side the inclusion of a Q.850 reason header in a response is not allowed.
Could I have some Guidance How I have to understand the following phrase written in RFC 3326 Reason Header:

   Initially, the Reason header field defined here appears to be most
   useful for BYE and CANCEL requests, but it can appear in any request
   within a dialog, in any CANCEL request and in any response whose
   status code explicitly allows the presence of this header field.

   Note that the Reason header field is usually not needed in responses
   because the status code and the reason phrase already provide
   sufficient information.

Does this mean that if I specify the use of SIP Reason in a response (e.G in a IETF RFC, ITU-T or ETSI Specification) it is allowed to use this now or do I need a special IETF draft to allow the use of Q.850 Reasons in responses?

Best Regards

Roland

Deutsche Telekom AG
T-Com Zentrale
Roland Jesske, TE332-2
Section TE33; Signalling, Gateways and Switching Systems 
 64307 Darmstadt, Germany
Phone:  +49 6151 83-5940 
Fax:      +49 6151 83-4577 
email:   r.jesske@t-com.net