Currently, if within a Template, a Viewbox is moved into a ToolBarOverflowPanel, the Viewbox gets deleted from the Navigator.
See attached video.

Note that this issue only occurs within a Template, and the same operation on a Page works as expected.

Repro Steps:

1) Create a Project containing a MainPage.xaml, and introduce a Button to the Page.
2) Right-Click on the Button, and create a new Template stored in the Document Root.
This will open the Button Template in the Template Dummy Editor.
3) Convert the Root Border into a Grid, and delete all children other than this Grid.
4) Introduce a ToolBarOverflowPanel into the Root Grid.
5) Introduce a ViewBox into the Root Grid.
6) Drag the ViewBox in the Navigator into the ToolBarOverflowPanel

Observe the Viewbox being deleted from the Navigator in the process.

Expected Results: Viewboxes can be inserted into ToolBarOverflowPanels.