Y!'s two sets of results

day to day switching

[GerBot]

I am now almost completely convinced that Yahoo is running two sets of results.
Day to Day I see my ranking change but there are only two different result sets.
My rankings seem to switch but so too do my back links, which leads me to believe there are two distinct sets of data.

My other observation is that one set is much older than the other.

My questions:
Has anyone else noticed this?
Will both sets eventually move to the newer results?
When the older results update, do we see the new results update accordingly?
Do anyone know the time cycle Y! currently operate on?