Qt::Popup window flag behave incorrect

On MS Windows when I make Widgets that are inherits QAbstractScrollArea to be popup by setWindowFlags(Qt::Popup) method call, that widgets became look as ppup widget but mouse button press outside the popup widget does not close them! Only switch to another application close such widgets. Direct QWidget subclasses works well, but QAbstractScrollArea subclasses does not, and only under Windows!