I hide window title:
cMainWindow::cMainWindow( QWidget* parent /*= 0*/ )
: QMainWindow(parent, Qt::CustomizeWindowHint),
{
}

and I have slot to maximize/showNormal the window
void cMainWindow::toggleMaximize()
{
isMaximized() ? showNormal() : showMaximized();
}

While I maximize window it overlapped taskbar as if I use showFullScreen()
How to solve this problem?