In windows and Linux system, call setWindowFlags(Qt::FramelessWindowHint | Qt::WindowMinimizeButtonHint), show different display effect

In windows and Linux system, call setWindowFlags(Qt::FramelessWindowHint | Qt::WindowMinimizeButtonHint), show different display effect. The code is: 

QDialog *pDialog = new QDialog(NULL);

pDialog->setWindowFlags(Qt::FramelessWindowHint | Qt::WindowMinimizeButtonHint); pDialog->setWindowTitle(QString("asdfs"));

pDialog->exec();

On windows, an untitled rectangle is displayed, but on Linux, the system title bar is still drawn. This leads to a problem，We have a scene like this： A customized frame is inherited from QDialog, and Qt::FramelessWindowHint is set to hide its title bar. A part of the client area is drawn into a title bar. However, when Qt::WindowMinimizeButtonHint is set, two title bars will be displayed. Why? How to solve this problem?