XMS IBytesMessage causing problems with split ZIP file

Question

Since upgrading MQ to "IBM MQ Explorer V9.1", the XMS libraries that always worked in previous versions have started behaving differently.

Essentially, the code still recognises the messages as IBytesMessage type, and successfully writes them to file via a Byte array, but the file itself, which is a split zip file, fails to reconstitute itself.

Here's the lions share of that code:

Dim FactoryFactory As XMSFactoryFactory = XMSFactoryFactory.GetInstance(XMSC.CT_WMQ)

            'Create a ConnectionFactory Object
            cfConnectionFactory = FactoryFactory.CreateConnectionFactory()

            'this variable will contain the full path of any file downloaded from MQ
            Dim strMQMessageOutputFileDestinationFilePath As String = ""

            'This variable will be used to evaluate whether the MQ Message Output file exists
            Dim fiMQMessageOutputFile As FileInfo = Nothing


            'Set various Connection Factory properties
            cfConnectionFactory.SetStringProperty(XMSC.WMQ_HOST_NAME, Me.HostName)
            cfConnectionFactory.SetIntProperty(XMSC.WMQ_PORT, 1414)
            cfConnectionFactory.SetStringProperty(XMSC.WMQ_CHANNEL, "SYSTEM.DEF.SVRCONN")
            cfConnectionFactory.SetIntProperty(XMSC.WMQ_CONNECTION_MODE, 1)


            cfConnectionFactory.SetStringProperty(XMSC.WMQ_QUEUE_MANAGER, Me.QueueManager)
            cfConnectionFactory.SetIntProperty(XMSC.WMQ_BROKER_VERSION, 0)


            'Create a new Iconnection object via the Connection Factory
            connection = cfConnectionFactory.CreateConnection()

            'Create a sesion via the Connection Object, using ClientAcknowledge mode
            'ClientAcknowledge is being used because it allows us to control precisely 
            'when a message should be removed from the queue
            session = connection.CreateSession(False, AcknowledgeMode.ClientAcknowledge)


            'Create a destination using the Session Object
            destination = session.CreateQueue(Me.mstrDestinationURI)

            destination.SetIntProperty(XMSC.DELIVERY_MODE, 1)

            'Create a consumer using the Session & Destination Objects
            Consumer = session.CreateConsumer(destination)

            connection.Start()

            'IMessage is the base class that is returned from the Consumer's Receive method
            Dim recvMsg As IMessage = Nothing

            ' Retrieve message from Queue
             recvMsg = Consumer.ReceiveNoWait

                     strFileNameFromMsg = If(Not recvMsg.PropertyExists("fileName"), "",
                     recvMsg.GetStringProperty("fileName"))

                    If TypeOf (recvMsg) Is IBytesMessage Then
                        'Binary Message
                        Dim msg As IBytesMessage = CType(recvMsg, IBytesMessage)
                        Dim buffer(msg.BodyLength) As Byte

                        msg.ReadBytes(buffer)
                        Dim content As String = Text.Encoding.UTF8.GetString(buffer)

                        'The PrepareDestinationFile Function will generate a unique file name for the new file
                        'and ensure that the file does not already exist on the drive
                        strMQMessageOutputFileDestinationFilePath = PrepareDestinationFile(strFileNameFromMsg)


                        'A FileStream object is needed to write a binary array to a file
                        Dim fsZipFile As FileStream = New FileStream(strMQMessageOutputFileDestinationFilePath, FileMode.Create)

                        'Write the contents of the Byte Array to the File via the FileStream object
                        fsZipFile.Write(buffer, 0, buffer.Length)
                        fsZipFile.Close()


                    End If

So, the code doesn't throw any kind of exception - the code still recognises the messages as IBytesMessage, but the files won't unzip correctly.

Oddly, If we use rfhutilc.exe, we can manually pull files provided we set the Write options as No Headers and not Include MQMD - but the code above always worked in the previous version of MQ / XMS

Any assistance you can provide would be very much appreciated.