Return three, receive three

I have been a Netflix subscriber continuously for 15 months. In that time, I have rented about 230 movies, so that's an average of 15 per month. I returned three titles on Monday, so that they were checked in by Netflix on Tuesday. You would expect my next three movies to come from the top three slots in my queue. They did. However, #2 and #3 shipped Tuesday, and #1 is shipping today (Wednesday). My #1 was not a new release, nor did it have a wait status. My guess is that it's because I got my #1 the last few times in a row. I'm still getting my #1, just a day later.