Graphics Framework doesn't support selection of items with shift modifier.
Scenario:
1. Click on item
2. Click on another item with Shift key pressed
Expected behavior:
Items that intersect bounding area of both clicked items should be selected.

Update:
See attached example.
All rectangular items on scene are selectable. So there are scenarios:

1. Click on item "2"
2. Click on item "5" with SHIFT key pressed
Expected result: items "3", "4", "5" are selected
3. Right after that click on item "1" with SHIFT key pressed
Expected result: items "1", "2", "3" are selected, items "4" and "5" are deselected

1. Click on item "12"
2. Click on item "24" with SHIFT key pressed
Expected result: items "12", "13", 14", "22", "23", "24" are selected
3. Right after that click on item "1" with SHIFT key pressed
Expected result: items "1", "2", "11", "12" are selected

In all described scenarios only one item are selected now, so SHIFT modifier does nothing for items selection.