Only on shift+down.

Suppose, we have item0, item1, ... etc

MultipleSelection, not single cell (whole row selection)

1. Click on item0
2. Shift+down
3. Shift+down - 3 items are selected.
4. ctrl+space - creates anchor, deselects item2
5. shift+down. - item0 is selected wrongly. All others - correct.

Affected tests:
ControlsAutomatedTestSuite/javafx/scene/control/test/treetable/TreeTableSelectionTest/keyboardShiftUpDownTest