I've tried all the above when the problem occurs.
What's most frustrating is that all formatting is fine when its posted for the first time, but when if I go back to edit a post, formatting and/or script for video is lost, sometimes.
Text formatting doesn't appear to be as unstable, but on almost every occasion when editing a post that contains video script, when I update the post, the video is lost.
I've had this problem with three different theme's, and I've tried deleting the entire post and reposting it, to no avail. Just to be clear, I would always start by entering the text into the 'visual' window and toggling to HTML to enter the video script, if this didn't work I've tried entering both the text and the script into the HTML, again to no avail.
I'm now reinstalling wordpress for the 5th time which appears to be the only thing that cures the problem.
Should I just resign tot he fact that I can't edit posts, or is there a fix. I've had the problem so many times now, I can't believe I'm the only one.