Windows limitation on overlapped buffer size, Error 87 Wrong Parameter

Observation: when communicating with a Linux g_serial based device from Windows 10 I get Windows error 87 "Wrong Parameter" if the QByteArray passed to QSerialPort::write is 4.2 MB or greater, but it works if 4.1 MB or smaller.

Analysis: _q_startAsyncWrite seems to hand over the original QByteArray 1:1 to ::WriteFile. The code does not assume any buffer size limitation and indeed I did not find any MS documentation or forum posts indicating such a limitation. But there seems to be one on Windows, even if undocumented. The issue does not occur on macOS. 

Work-around: I can avoid the Windows error using the following adapter:

static int serialWriteAdapter( QSerialPort* port, const QByteArray& buf ){
#ifdef Q_OS_WIN 
    const int winBufferSizeLimit = 4100000;
   int i = 0; 
   while( i < buf.size() ) {
       const int res = port->write( buf.mid(i,winBufferSizeLimit) );
       if( res < 0 ) return -1;
       i += res;
    }
    return i;
#else
    return port->write(buf);
#endif
}

The work-around also works on Windows 7.