Details panel for inner mesh component is blank

Hello, I asked this question on answershub but noone replied to me, so may be people on the forum know what the problem is:
answerhub question

So I created a class based from AActor, then I created a component class based from USceneComponent. Then I put the component (TestComponent) inside actor class and also added static mesh component (TestMeshComponent) to my scene component:
ATestActor -
----UStaticMeshComponent SomeMesh
----USceneComponent TestComponent
--------UStaticMeshCOmponent TestMeshComponent.
The code for 4 classes attached

Now I created blueprint which is based from ATestActor. And here is the problem - When I open that blueprint editor I cannot edit TEstMeshComponent. Its details panel is just blank. I cannot move, cannot change the properties, etc.
This is how it looks like:

What is my mistake?

p.s. UE version is 4.7.6

Thanks,