This same thing is happening to me right now. I have two projects: One in English and one in German and they are getting totally different results.
I have pretty much tried with everything: wistia, vimeo and dailymotion I got all of the videos on my sitemap BUT they were indexed in different times: first two of them and then the last one. I have noticed that sometimes Google shows the video snippets and sometimes its ignored.
The rankings for those keywords are being also very unestable. I tried also to put flash videos on my German language project and they also got indexed because I put them on my video sitemap but now in this precise moment I was testing if putting a video for a page that was on first position could get a higher CTR with the video snippet but guess what... currently my #1 ranking position is now out of the 100 positions. CHAOS!
I guess at this moment Google is trying to figure out whether to show up or not a video snippet and our page for a keyword in a language where there were never a video snippet. SO Confusing! Also found out that your rankings definitely drop when they were at the top 3 positions even they can drop to the second or third page but at this moment they are trying to get their past position. I will have to keep a big eye on this.
If you guys got more insight and ideas for me to get my video snippets with more stability let me know!
P.S in case you want to check my keyword and URL that was #1 and dropped out of the 100 results its the German word "Peru Reisen" my page is http://www.viventura.de/reisen/peru
Thanks