Mouse press / release issue on window border

If I move the mouse over the window border, until the mouse cursor is changed to the resizing cursor, then perform a click, I get both mouse events after releasing the mouse. 

I think the events should not be delivered at all in this case.

How to reproduce: 

I loaded the Window Flags Example, added this code:

previewwindow.h:

void mousePressEvent(QMouseEvent *event);
void mouseReleaseEvent(QMouseEvent *event);

previewwindow.cpp:

void PreviewWindow::mousePressEvent(QMouseEvent *event)

Unknown macro: {   qDebug() << "PRESS!!"; }

 

void PreviewWindow::mouseReleaseEvent(QMouseEvent *event)

Unknown macro: {   qDebug() << "RELEASE!"; }

Then start the application, and click once the preview window (to bring it into focus), then move the mouse to the border of the frame until the mouse cursor changes to resize cursor, then click. In the application we can see that the two events (mouse press and release) are delivered together. 

It only reproduces right after starting the application, until the application first looses focus.