Using the C++ SDK, how do I decode and re encode all messages except some Activity records which need correction

Has anyone worked with the C++ SDK enough to explain MesgListeners to me?

It appears that I can AddListener an Encode object which implements MesgListener to the MesgBroadcaster which I pass to Decode::Read.

Since Encode::OnMesg just contains Write(mesg), this causes all recognized decoded messages to be re encoded to the output file.

In addition, I would like Decode to call the OnMesg of a special RecordMesgListener for record messages rather than Encode::OnMesg so I can correct some records.

However, when I AddLIstener a stub RecordMesgListener to the MesgBroadcaster which just does Write(mesg) like Encode::OnMesg, I do not see identical output  as I would expect.

Instead, I get an output that has some additional (but not duplicates of all) records and other corruption and a bad CRC.

Why is this happening?

Here's my Recode function:

int Recode(Listener& listener, fit::MesgBroadcaster& mesgBroadcaster, char* filename)
{
    // Open file to decode
    fit::Decode decode;
    fstream inFile;

    inFile.open(filename, ios::in | ios::binary);

    if (!inFile.is_open())
    {
        printf("Error opening file %s\n", filename);
        return -1;
    }

    if (!decode.CheckIntegrity(inFile))
    {
        printf("FIT file integrity failed.\nAttempting to decode...\n");
    }

    // Open the file to encode
    std::fstream outFile;
    outFile.open("badFileRecode.fit", std::ios::in | std::ios::out | std::ios::binary | std::ios::trunc);

    if (!outFile.is_open())
    {
        printf("Error opening file badFileRecode.fit\n");
        return -1;
    }

    // Create a FIT Encode object
    fit::Encode encode(fit::ProtocolVersion::V20);

    try
    {
        // Write the FIT header to the output stream
        encode.Open(outFile);
        // Allow the RecordMesgListener to encode after fixes
        listener.encode = encode;
        // Other decoded messages are written by encode without changes
        mesgBroadcaster.AddListener((fit::MesgListener&)encode);


        decode.Read(inFile, mesgBroadcaster);
    }
    catch (const fit::RuntimeException& e)
    {
        printf("Exception decoding file: %s\n", e.what());
        return -1;
    }
    catch (...)
    {
        printf("Exception decoding file");
        return -1;
    }


    try {
        // Update the data size in the header and calculate the CRC
        if (!encode.Close())
        {
            printf("Error closing encode.\n");
            return -1;
        }

        // Close the file
        outFile.close();

        printf("Encoded FIT file badFileRecode.fit.\n");
        return 0;
    }
    catch (...)
    {
        throw std::exception("Exception encoding activity file");
    }
}

Here's the Listener specific to RecordMesg

class Listener
    : public fit::RecordMesgListener
{
public:
    fit::Encode encode;

    void OnMesg( fit::RecordMesg& record ) override
    {
        encode.Write(record);
    }
};