Use or abuse of [reply endpoint] property?

[Alastair Green <alastair.green@choreology.com>]

A question (cluster of questions) has arisen in the OASIS WS-TX TC re 
use of WS-Addressing.

App A sends message "a" to app B, who may send "b" to A at a later time, 
in an exchange where "a" and "b" are logically related (form part of an 
exchange or conversation) at an application level.

A possesses, a priori, an EPR for B (B.E) and likewise B possesses an 
A.E, and these can be used to target the messages "a" and "b".

Message "a" contains a non-anon, non-none value for [reply endpoint] 
[address], A.E'.

B chooses to ignore that value and sends "b", not to the new potential 
target A.E' but to A.E. The A-B application-level contract defines "b" 
not to be a "reply" to "a", but merely a one-way message that is, if you 
like, in apposition to "a".

B can also choose (at its whim, in any given execution of this exchange) 
to send "b" to A.E', and not the old target A.E.

Q.0. Is this a legitimate use of the [reply endpoint] of "a"? 
Spiritually? Legally?

Related questions:

Q.1. Must message "a", having a [reply endpoint] value, therefore set a 
[message id] value, or can this latter property be omitted in the 
representation?

Q.2. Closely related to Q.1. Can B ignore this message id even if it is 
present, and refuse to express (omit) the [relationship] of its message 
"b" to the original "a" message, in the case where it chooses to target 
"b" on new reply target A.E'?

Q.3. If message "a" desires no reply, should message A set [reply 
endpoint] [address] to the "none" URI? Is the "none" value for this 
property the effective definition of a "one way message" (one that gives 
no indication of expected future interchanges)? Is the "none" value the 
only circumstance in which the [message id] can be omitted?

Q.4. Closely related to Q.3. If the [reply endpoint] is instead omitted 
in "a" and the property is therefore inferred on receipt by B to be 
anonymous, what should B send in the underlying transport response if it 
wishes to send no reply at an application level?

Close reading of 2004-08, the CR and the latest editors working draft 
leaves me unable to answer these questions unambiguously and unaided. 
That may well mean I'm missing something obvious or fundamental, but 
help would be greatly appreciated.

Many thanks for any elucidation that the WG and other users of this list 
can offer.

Alastair