Currently, in a situation where the ContentPresenter Element has been removed from the ListBox ItemContainer Template, the assigned ListBox Item Template can be accessed, and opened from the Resources Panel.

However, when a ListBox Item is attempted to be opened for Edit from a Page/Template, it fails to open the ListBox Item Template in the Inline Dummy Template Editor.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml

2) Introduce a ListBox to the root Grid.

3) From the Stage, right-click on the ListBox Element, and create new Templates for the ListBox ItemContainer, and the ListBoxItem (ensuring both are assigned to the ListBox Element introduced in Step 2)).

4) From the ListBox ItemContainer Template, remove the ContentPresenter found in the default Template.

5) Exit all open Dummy Template Editors, and return to the root of MainPage.xaml.

6) Right-click on the ListBox on the Stage, and navigate to 'Templates' --> 'Item' --> 'Edit'

Observe how the ListBox Item Template fails to open inline.

7) Navigate to the Resources Panel, identify the ListBox Item Template, hover over it, and click the 'Pencil' icon to edit it in the Isolated Template Editor.
Observe how the Template opens as expected.

Expected Results: When a ListBox Item Template is attempted to be opened from the Page, and a ContentPresenter is missing from the ItemContainer, a warning toast should appear that reads something along the lines of:

Title: "Unable to open inline Template"
Description: "The assigned ItemContainer Template requires a ContentPresenter to display its Item Template."