Currently, if editing a Data Template, and a non-default (1920x1080) Design Size is set for it, when hitting 'Play', the active Page will render at the Data Template's Design Size rather than the active Page's Dimensions.

Additionally, when editing a Data Template, when 'Play' is pressed, the Data Template's Design Size Adorners will be visible on-Stage.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml

2) Introduce a ContentControl Element to the Page's root Grid.

3) Right-click on the ContentControl, and create a new ContentControl Content Template, saved in GlobalResources.
This will open the Template in the inline Template Dummy Editor.

4) Exit the Inline Template Editor and return to the MainPage.

5) Navigate to the Resources Panel, and under GlobalResources.xaml, identify the ContentControl Content Template created in Step 3.

6) Hover over the ContentControl Content Template, and click on the Pencil icon to edit it in the Resource-based Template Editor.

7) Set the green DesignSize adorners to 64 each.

8) Hit 'Play' at the top of the application window.

Observe how the Page is displaying at the 64x64 DesignSize Dimensions of the Content Control.
Observe how the green DesignSize Adorners are visible on the Page.

Expected Results: Hitting 'Play' always renders the Page at the active Page's size, not the opened Template's size.
Expected Results: Playing a Page never displays edit-only adorners.