It's not getting submitted twice. That's just the text link because the thumbnail for the video failed to generate. Don't worry about it, it happens to me when I submit videos too (I think it has something to do with MPG videos maybe) but it doesn't mean it submitted twice.
Oh that's what you meant. Yea I haven't figured out why that is happening exactly but every week or so I fix the videos that it happens to. So you're image should be showing up in a few days.