I am having the same problem. Embedding YouTube videos on a page (actually any page as I have tested it with 4 of them), and as soon as someone visits the page, the embed code is deleted and a entry is made in the revisions list with no author.
Strange thing is, this only happens on Pages and not Posts. Also, an old page that I have not edited since version 3.4.x has embed code that is still working.
Running WP 3.6 and have disabled all plug-ins. Have recreated this error over and over again.
