Thumbnails Don't Showing in My Theme

Hi, i am using Templatic Video theme which is here: http://templatic.com/app-themes/wordpress-video-theme

and my website is http://videocu.tv

in the theme documentation it written like this: http://prntscr.com/4aa30g so it must be work with this theme.

when i insert youtube url in the debugging page to the “Test Markup for Video” section after when i scanned for that url, i see thumbnail of that video. And also i can download test thumbnails.

But after posting a video, thumbnails of video don’t come. I asked to the developers of templatic. I wanted to ask here too. Please help me for solving this problem.