The result in position 4 has been rotating between three different firms all day for our industry's top value keyphrase. All other listings above and below remain constant.
That's a very interesting observation - however, it is a different pattern than the #6 bug. That one accidentally demoted a large number of urls from top positions to exactly #6. I'm not seeing this one yet, but I'll keep an eye out. I don't usually check the same SERP frequently enough to catch a pattern like this.