Currently, if you have a custom ResourceDictionary_B merged into another ResourceDictionary_A, and you delete the XAML file completely for ResourceDictionary_B, it will continue to show in the Resources Panel as still existing, and still being merged into ResourceDictionary_A.

This issue occurs whether in the example above ResourceDictionary_A is a GlobalResources dictionary, or a manually-created one.

This issue generates a XAML error, but that only manifest once the application is rebooted, and not at the time the error occurs.

Repro Steps:

1) Create a Studio Project featuring a MainPage.xaml

2) From the Assets Panel, create a new file of type 'ResourceDictionary', and give it a unique name on creation.

3) Navigate to the Resources Panel, and merge this new ResourceDictionary into GlobalResources.xaml
This should open the GGlobalResources.xaml file in its own tab. However, if it doesn't, manually open the GlobalResources.xaml file to have it open in order to monitor it in future steps.

4) Return back to the Assets Panel, and delete the ResourceDictionary created in Step 2).

5) Navigate back to the Resources Panel.

Observe how the ResourceDictionary that was deleted from the Project, is still showing as an existing, merged ResourceDictionary.
Observe how no XAML errors are being displayed.

6) Save all open documents, then close and re-open the Studio application.

8) Open the GlobalResources.xaml file.

Observe how now, XAML errors are being displayed.

Expected Results: ResourceDictionaries deleted from a Studio Project no longer show as Merged Dictionaries in the Resources Panel.
Expected Results XAML errors display as soon as the error is detected, and doesn't require a reboot to manifest.