C# wrapper Custom UI

Please can you explain to me the differences in use of VideoRenderElementType.

When I use the CreateVideoElement (VideoRenderElementType.VideoRenderElement_ACTIVE) I correctly get the video of the person who is currently speaking on the screen. I create this in the onMeetingStatusChanged event when the meeting status is “MEETING_STATUS_INMEETING”.
In the cases of VideoRenderElementType.VideoRenderElement_NORMAL or VideoRenderElementType.VideoRenderElement_PREVIEW I get only a black region.

I used C# wrapper v5.0.24433.0616