FMaterialRenderProxy objects are not deleted when switching to an empty scene

Hello everyone, I’m developing a module for UnrealEngine and faced a problem with UnrealEditor.
If I open a scene in the editor, it loads the materials and creates FMaterialRenderProxy instances. Then, if I switch to a completely empty scene the objects are not deleted. If I open the material editor and scroll through all the materials available in the dropdowns it creates even more of the material render proxy instances which are never deleted. So I have 3 questions:

  1. Why the objects are not deleted if they are not used in the scene?
  2. Is there a limit on the number of unused FMaterialRenderProxy objects that can exist at the same time?
  3. Is there a mechanism to manually force these objects to be deleted if they are not used in the scene?