To reproduce: open the VirtualGrid >> First Look example in QSF and follow the steps:

1) I have a virtual grid which has both vertical and horizontal scroll bars.

2) Scroll to the very bottom of the grid

3) Select the last row

4) Scroll all the way to the right

At this moment the selected row disappears from the view. While scrolling horizontally the vertical scrollbar jumps several rows above although it seems scrolled to the bottom.