David, not too long ago (or least I didn't notice it until very recently) Your plugin began to cause strange behavior on WordPress sites. For instance on 1 on of my posts (not the rest however) the behavior described by the OP began to appear. I use your plugin for a single PAGE on my site, yet this error appears on a single POST un-related elsewhere on the site. I don't know why.
If you google "preg_match() Delimiter must not be alphanumeric or backslash in media.php wordpress" you will see that is affecting pretty much anyone using your plugin.
Steps to recreate are (at least for me) impossible to determine. Again, I just use your shortcode on a single page on my site, and it affects another post somewhere else (without any shortcode or youtube, etc).
Oddly enough, I opened up media.php in Dreamweaver to debug the $url being passed (Seems like an unescaped literal being passed to the preg_match) and just SAVING my file made my errors go away, which blew my mind.... don't ask me.
Anyways, this is the best help I can get to you at this time, since my issues went away the second I tried to narrow them down. Hope this helps a bit... sorry brother.