eb:RefToMessageId in one-way pull request responses

The core spec, ebms-core-3.0-spec, shows clear examples of pull request responses containing an eb:RefToMessageId. However, in section 2.2.6 'The One-way/Pull MEP' states the following

'To conform to this MEP the pulled User Message unit MUST NOT include an eb:RefToMessageId element.'

In AS4 the support for MEP is one-way, with support for two-way MEPs being somewhat ambiguous.
Is eb:RefToMessageId relevant in the case of one-way MEPs ie. a one-way response need not be based on any previous business message ?

In the case of signed queued messages (awaiting a pull request) eb:RefToMessageId cannot be used as it will break the previous signature. 

Our take on this is that 2.2.6 is correct for one-way MEPs.

Further thoughts/comments/clarification on this appreciated.

-- 
Regards
Theo