In Unreal Editor, adding a UCustomComponent to any actor using the “Add Component” button, adds the UCustomComponent and attachs a UBoxComponent as its child (with ‘(Inherited)’ appended), as expected. Clicking the UBoxComponent, in between the details and components panels it reads: “Native components are editable when declared as UProperty in C++”. Right-clicking → deleting does not delete that component. If I delete its parent, the UCustomComponent, it still cannot be deleted. The only way to get rid of it is to delete the entire actor, which is counter-productive.
I will verify in several days whether this behaviour also occurs in the latest version of Unreal Engine.
I am marking this topic as resolved for tracking purposes. If you are able to determine the repro steps, feel free to post a response to this topic. For any new issues, please create a new Answerhub topic.