UActorComponent* variable with Instanced can't save in blueprint

Here is the code write in my custom character header file:

UPROPERTY(EditDefaultsOnly, Instanced)
UActorComponent* TestComponent;

I can edit it and I can use this component too. But when I reopen editor, I get this:

Who know what’s the problem is?

You can’t assign component pointers from Details panel.
They won’t show up in a dropdown list.

But it work fine on UE4.5, maybe Epic remove this.