iTunes video thumbnail problem

[QueBert]

I tried to Google this but I'm not sure what to search for. If I buy 3 music videos from the same artist, all 3 pics in coverflow will be the same screen from the same video. It's not showing 1 per video, it just stays on the same thumbnail. If I right click while it's playing and "set poster frame" it doesn't change. Is this normal? I'm not sure how iTunes works for videos, but I would think each should get it's own pic.