Cursor key navigation in item view causes wrong selection

If a view has a delegate that sets a different height for the current item, then QAbstractItemView::keyPressEvent() causes selection to change twice: First to the correct item and to some random one. It seems that the code that calculates the new selected rectangle mixes the old and the new height somehow.
The attached project demonstrates the issue both visually and with debug output: Just use the arrow-down key to go through the list items.