On Windows QtSerialPort misses EV_TXEMPTY in event mask. That is why if such an event occures, QtSerialPort will treat it as error. This even is correctly treated on WinCE.

The solution is to edit qserialport_win.cpp and add the missing event to the originalEventMask.

In bool QSerialPortPrivate::open(QIODevice::OpenMode mode)

...
if (mode & QIODevice::WriteOnly)

{ desiredAccess |= GENERIC_WRITE; originalEventMask |= EV_TXEMPTY; }

...

Please commit it with reference to my nickname.

Thanks
Arokux.