http://www.moneynews.com/MKTNews/billionaires-dump-economist-stock/2012/08/29/id/450265Hard to know if it's a trend, but the reasoning sounds about right.
Although a collapse might not seem likely when they're still printing money, the critical point is usually when the printed money starts to become less effective as a tool to stimulate growth. The first indicator of this would be where savvy investors start pulling back from the markets, having already soaked up much of the easy money. This article seems to indicate just such a pull back from the American market at least.
Author