Coordinate transformations might be tricky...Here is a code snippet i used long time ago...and the thing is that i'm not sure if i figured it out completely back then...cuz i had the same problem.

Qt Code: 
  1. //..
  2.  
  3. view = new QTableView;
  4.  
  5. // ...
  6.  
  7. void Widget::customContextMenuRequested(const QPoint &point)
  8. {
  9.  
  10. QModelIndex index  = view->indexAt(point);
  11.  
  12. 	if( index.isValid() )
  13. 	{
  14.  
  15. 		QPoint viewPortPosition = view->pos();
  16.  
  17. 		int headerOffset = view->horizontalHeader()->sectionSize(0);
  18.  
  19. 		int adjustedHeight = viewPortPos.y() + headerOffset;
  20.  
  21. 		viewPortPos.setY(adjustedHeight);
  22.  
  23. 		QMenu menu;
  24.  
  25.                 // ...
  26.  
  27. 		menu.exec( mapToGlobal(QPoint( viewPortPos + point )  ) );
  28.  
  29. 	}
  30.  
  31. }
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Even thought i've used QTableView , i'm sure it's gonna give you an idea...If you find that there is something wrong with my implementation (i'm sure there is) , i'd be glad to hear the right way to do it!^^