CompositeVideoClip of CompositeVideoClips does not provide expected behavior.

[davidbernat]

Expected Behavior

video = CompositeVideoClip([background, overlays])

When background and overlays are both CompositeVideoClip objects, the resulting new composite will often fail to contain the video elements of the latter. If, instead, the new composite is created using this code, the expected result occurs; however, under-the-hood functionality of true composites may be missed.

video = CompositeVideoClip(background.clips + overlays.clips)