Repro Steps:
1) Create a Page
2) Introduce two elements to the RootGrid of the Page
3) On the Stage, hold [Shift] and select one of the elements.
Observe the selected element receiving a blue outline, representing its selection.
4) Still holding [Shift], select the other element.
Observe how the first item no longer has its blue outline, and only the newest item receives it, making it appear as though the first item has been deselected, when in fact, when looking at the layer in the Navigator, it is still selected.
Expected Results: All items maintain a blue outline whilst selected as part of a multi-selection. | 
