SOAP 1.1 defines the attribute "actor" that can be on any SOAP header which will indicate who the ultimate processor of the header is going to be. It also defines a standard URI value for this actor attribute that is "http://schemas.xmlsoap.org/soap/actor/next" which implies that the header is intended for the very first SOAP application that processes the message. The absence of the actor attribute would mean the same as well.
SOAP 1.2 renamed this attribute to "role". But the semantics remanis the same as SOAP 1.1.
WCF Security does not recognize this attribute. WCF will not emit this attribute in the Security header element in any messages it emits. If a received message contains a actor attribute in the Security header the header will not be recognized even if the value is set to http://schemas.xmlsoap.org/soap/actor/next. You will see an exception that says "No Security header present in the message.". To work around this do not emit this attribute in the Security header in your messages to WCF.