Marathon has done a lot of experimenting with videos on websites.
Though not nearly as technical, I've had my own little experiments and mishaps with the simple process of uploading html code to this site. Here's my experience with this WordPress site.
The first time I uploaded a youtube video to this site, it worked swimmingly. Too easy! Then I went to edit it, and the video just disappeared. After several attempts to bring the video back, I tried clicking "save" from the Code tab (rather than the Visual tab.) That worked.
Since then I've had the same trouble with other HTML code besides video. If an edit is needed, it has to be published or saved in the "Code" mode. Just a WordPress glitch. Thankfully the workaround is simple....if only I can remember it in time of need. - milkmaid