Can only replicate this issue on IE10
In Lessons, click add multimedia.
Enter in a youtube URL, such as http://www.youtube.com/watch?v=hg3Uyk8noWM
Click edit on the multimedia item, the video will stay on top and the edit screen will be behind the video. If you click add multimedia again, or add resource/question/etc, the video will always remain on top and the other information behind it.