QMessageBox in mousePressEvent causes infinite loop (Mac)

Derive a MainWidget from a QWidget, set is as central widget of a QMainWindow, and provide the following method:

void MainWidget::mousePressEvent(QMouseEvent* pEvent) {
  QMessageBox::warning(this, "Title", "Hint");
}

Then,
1. Click the RIGHT or MIDDLE mouse button inside the MainWidget (left button works fine)
2. Close the appearing message box by CLICKING on the Ok button (closing per keyboard works)
-> When you now move the mouse inside the MainWidget (without clicking), the message box re-appear, again and again as infinite loop.

Also, if you close the message box in step 2 per keyboard, the message box doesn't appear again when you move the mouse, but if you press the right button again, it doesn NOT appear again, until you click a 3rd one.

I can reproduce this on my Mac (OS X 10.7.4), but on Windows all works fine.