Our site 1sttalk.com has blog-mu theme. When I show a picture with lightbox, the background youtube video comes to front and blocks the picture.
You can test it by logging on the site via your Facebook credentials. Just go to this link and click on a RSS feed on the right while the youtube image is on the display. https://1sttalk.com/groups/turkiyem/
I will post a screenshot in the next update.