Well, Ive' reimplemented mousePressEvent in a following fashion:
Qt Code: 
  1. void MerchandiseWidget::mousePressEvent (QMouseEvent* event)
  2. {
  3.     if(event->button()==Qt::LeftButton)
  4.     {
  5.         if(windowState()==false)
  6.         {
  7.             resize(QSize(WIDGET_WIDTH+WIDGET_WIDTH_DELTA, WIDGET_HEIGHT+WIDGET_HEIGHT_DELTA));
  8.             setResizedState(true);
  9.         }
  10.         else
  11.         {
  12.             resize(QSize(WIDGET_WIDTH, WIDGET_HEIGHT));
  13.             setResizedState(false);
  14.         }   // if
  15.     }   // if
  16. }
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Now, the widget gets resized, but if I click on it again, it does not get smaller. Can you please tell me why?