It is expected that pressing SHIFT-UP and SHIFT-DOWN will extend or contract the selection by one item up or down.

Steps to reproduce:
1. launch HelloTreeView app
2. click Child Node 7
3. press SHIFT-DOWN to add Child Node 8 to the selection
4. press SHIFT-UP to remove Child Node 8 from the selection
RESULT: Child Node 8 remains selected and only focus is moved. Pressing SHIFT-UP again will extend the selection so Child Node 6 - Child Node 8 are selected.