Cannot assign a MediaTexture asset to a Brush -> Image in Widget Blueprint

Can't assign Media Texture assets to the Brush->Image property in Images on Widget Blueprints. This workflow is explicitly mentioned as a step in these docs, so if this is no longer the correct method and/or a step is missing, those docs should be updated as well. 

• Create a new widget blueprint
• Add an image to the widget blueprint
• On the details panel of the image, attempt to assign a Media Texture asset to the field Appearance->Brush->Image, either through drag and drop or typing in the asset name

Expected Result:

• You should be able to assign a Media Texture asset to the image, and/or a clear warning should appear in the logs

Actual Result:

• The outline of the property is red when dragging and dropping, and the name of the asset does not appear in the search