Windows Live Local Bird's Eye Imagery

I was playing around with local.live.com's Bird's Eye view again, and noticed that they have multiple sets of data online at the same time. That is, you don't always get the exact same photo each time you view an area.

I would expect that as you change the view to spin around North, East, South, and West that the times of day, and even maybe the time of year might change. But, I noticed while spying on my house that sometimes the year itself that the picture was taken for any given view changes! I can't figure out when it decides which picture to show, either.

Examples:

All three of these are "South-facing" views of my house.


This one was definitely taken before the fall of 2004, because the big spruce tree between the two houses was cut down then.


This one was taken on a Friday morning (garbage day--see the cans by the street?) in what I would say the spring of 2005 (the spruce tree is gone, but leaves are not on any of the trees yet. Also, my red-roofed neighbor had not yet let himself into my backyard to clear away the leaves that I left there over winter).


And this third one was probably taken on the same day as the second picture, only in the afternoon (no garbage cans, and the shadows are casting eastward).