Repro Steps:

1) Create a Page
2) Within the Page's RootGrid, introduce a Grid, and name it "Grid1"
3) Within the Page's RootGrid, introduce a second Grid, and name it "Grid2"
4) Introduce multiple elements to the Grid titled "Grid1" -- they can be any elements, and as many as desired. (In my case however, I did 6 Canvas Elements)
5) Using [Ctrl+Click], or [Shift+Click], select every element that was put into Grid1 in Step 4). You should now see every element within Grid1 selected in the Navigator.

6) In the Navigator, click-and-Drag the multi-selection from Grid1 to Grid2.

Observe how only a single element is moved to Grid2, and the rest stay behind in Grid1.

Expected Results: Clicking-and-dragging a multi-selection to another layer in the Navigator moves the entire set, and not just a single element.