Just deleted a post because without the embed code it made no sense. Somewhere between previwing the post (in which the video was clearly visible and working fine) and the actual publishing, the code vanished. Very strange. I've had videos turn into blank spaces labeled that the video is no longer available, but I've never had a line of html disappear from a post that had been saved.
Technology. Like the S.O. says, it's fucking magic.