The current implementation of the Soap11DataFormatAdapter and Soap12DataFormatAdapter will never generate SOAP Headers when a JAXB object is the inputObject.
If the unmarshal is done with ignoreUnmarshalledHeaders set to false, then the SoapJaxbDataFormat.SOAP_UNMARSHALLED_HEADER_LIST message header is populated with a list of Objects or JAXBElement<?>s. However, during the doMarshal, this message header is never referenced. Therefore, the sequence:
will never produce SOAP Headers in the outbound document.
The doUnmarshal passes the inputObject and an empty List<JAXBElement<?>> into createContentFromObject. However, is the inputObject is an ordinary JAXB object (or JAXBElement<?>) then no header content will be created, and since the Exchange isn't sent to createContentFromObject, the SoapJaxbDataFormat.SOAP_UNMARSHALLED_HEADER_LIST cannot be referenced.
It seems to me that, if ignoreUnmarshalledHeaders is false, and the SoapJaxbDataFormat.SOAP_UNMARSHALLED_HEADER_LIST is non-empty, and in the event the inbound Exchange does not contain an Exception, then the contents of the SoapJaxbDataFormat.SOAP_UNMARSHALLED_HEADER_LIST should be added to the headerContent before the call to createContentFromObject.
I have checked the code for SoapJaxbDataFormat, Soap11DataFormatAdapter and Soap12DataFormatAdapter from camel-soap 2.12.0 through 2.15.2 and it looks like these three classes haven't changed.
I crated a demo project and patch, originally against JBoss Fuse 6.1.0, but offer it here for the camel-soap 2.12.x branch. I have also applied and tested the patch against camel-soap in the master branch (2.16-SNAPSHOT). Indeed, it looks like this patch can be applied from any point 2.12 and forward.
The demo can be run against 2.12.5 (or any released version - just change the camel.version property in the POM) to demonstrate what I think is the failure. It can also be run against a patched 2.12.6-SNAPSHOT or 2.16-SNAPSHOT (again, just play around with the camel.version property) to demonstrate what I think is correct behavior.