It might just be that MSN is trying different things to produce better SE results.

I was on top with Google in a very competitive subject and then poof - gone. In panic I emailed Google and they said it might just be there bot or other issue - not all to clear - of course they are not going to say much or do much.

However, within 3 weeks I was back in the top results, but slightly better - so it is possible that some restructure or programming changes at MSN might cause a prob - maybe?