request for clarification

Jim,
here is another request for clarification:

The following phrase is a cut and paste from the metamodel document.

A responding role that throws a business protocol exception signals the
exception back to the requesting role and then terminates the commercial
transaction. A requesting role that throws a business protocol exception
terminates the transaction and then sends a notification revoking the
offending business document request. The requesting role cannot send a
business signal to the responding role.

The last sentence says the requesting role cannot send a business signal to
the responding role. I had previously understood that to mean never, ever. But
now I am wondering if it is only within the context of the paragraph. The
reason for this question is that in the patterns I see requesting roles
sending receiptAcknowledgement signals. So a follow-up question is are
receiptAcknowledgement from the responding role sometimes, never, or always
required (or allowed)?

thanks,
-karsten