UMLR — Reply messages now mandatory?

until UML 2.3, the spec said about reply messages: “If the Message represents a CallAction, there will normally be a reply message from the called Lifeline back to the calling lifeline before the calling Lifeline will proceed.”

Did the initial submission team agree on making reply messages mandatory?

I’m just asking because the above mentioned sentence was removed (actually already by UML 2.4 RTF) and there is only one example listed in the current spec for synchronous calls showing reply messages, and also the semantics of Message indicates that reply messages are mandatory from now on.

Tool vendors commonly not enforce the existence of reply messages for synchronous calls.