When a Page is the currently-open document in Studio, with the Data Panel open as well, its Structures, Enums, and Sets can all be selected to reveal their Properties in the Properties Panel.

However, when a Resource document (such as GlobalResources.xaml) is instead open within Studio, the Data Panel continues to be accessible, but selecting Structures, Enums, or Sets, does not successfully open their associated Properties Panels, and instead forces the Resource Documents Properties Panel until a Page is set as the active/open document instead.

See attached video.

Since Data is not associated with any Document in particular, and instead resides at the Project Level (and is not even a part of the Project's XAML files), it is a bit difficult to understand why the document type currently open would impact the ability to view, or edit any Data items.

Repro Steps:

1) Create a Studio Project containing a MainPage.xaml

2) Navigate to the Data Panel, and create any collection of Data Structures, Enums, and any desired Data Sets for the Structures.
Observe how with MainPage.xaml open and active, everything in the Data Panel is accessible and editable.

3) Navigate to the Assets Panel, and create a new Resource Dictionary.

4) Open the document of the Resource Dictionary created in Step 3), ensuring it is the currently-active tab in Studio.

5) With the Resource Document still open/active, navigate back to the Data Panel, and click through any of the Data Items created in Step 2).

Observe how none of the Properties of any of the Data Items selected can be exposed in the Properties Panel.

Expected Results:
Data Structures, Enums, and Data Sets for a Project can be always be accessed and edited no matter which document type is currently open on the Stage.
OR
The Data Items in the Properties panel have their ability to be 'selected' in the Data Panel removed, if they are clicked with a Resources Document open.