Serial works in LabView and not in C++

Question

Hey,
I’m using Qextserialport 1.2 alpha in my project. (QT C++ programing)
I got invalid data when I use other windows application while I’m recording the data at hight rate of 400hz.
BUT, when I first open the port via HyperTerminal or LabView and then I connect throw my SW, the problem is vanished.
The problem doesn happend in low rate (1h,10h)
Any Idea?!?
port = new QextSerialPort(portName,QextSerialPort::EventDriven);
if(!port->open(QIODevice::ReadOnly )) {
qDebug("Cannot open serial port: %s Error: %s",
portName.toAscii().constData(),
port->errorString().toAscii().constData());
return -1;
connect( port, SIGNAL(readyRead()), this, SLOT(onReadyRead()));
port->setBaudRate(BAUD921600);
port->setDataBits(DATA_8);
port->setParity(PAR_NONE);
port->setStopBits(STOP_2);
port->setFlowControl (FLOW_OFF);
port->setRts( true );
port->setDtr( true );
My setup:
Win XP sp3
QT 4.7.0
Thanx!

Answer 1

Thanks for your replay.
I'll try to be more clear about what I mean in "windows application".
While I'm recording data with my SW, each change that happened i.e. maximize or minimize the SW window or opening other document can damage the recording data.
This doesn't happened when I first open the LabView SW then connect and disconnect from the serial comport.
And then open my SW, connect the serial port start recording data and I can maximize or minimize the SW while recording and it won't damage the record.
P.S. I need to record the data with my SW and not with LabView.