The usual algorithm calculates a score, ranks the questions and then just pulls off the top few results.
We're testing an alternative method that calculates a score, ranks the questions and then pulls a somewhat larger number off the top, shuffles them, and stuff the top of the deck into the sidebar.
Since this is a test, not everyone will see this. Those who do will observe both a larger variety of questions, a less predictable order for those that do show up repeatedly and a greater chance of seeing different questions on different page-loads.
And since this is a test, it may end up having horrible side-effects that result in it being tied up in a sack with a brick, thrown off a bridge and never spoken of again.