Not sure what's causing this (or what's happening).
The first thing to do when you encounter UI issues that persist after closing and restarting Aperture is to delete your user preferences. Details on how to do this are on Apple's Aperture trouble-shooting page.
Is the thumbnail being moved? Does the selection change to a different thumbnail? Or is it simply that the view changes to show the top-most thumbnail?
In Places view, clicking a pin selects all the Images associated with that pin. Clicking a pin with Images already selected will de-select the selected Images and select the Images associated the the clicked pin. Clicking the map, but not a pin, deselects all Images. That's by design. What are you trying to do?
Thanks for your thoughts and ideas!
As far as I can tell, the scrolling behavior is not a malfunction, since every version of Aperture has had this behavior.
I try to keep all my images geo-tagged, and often end up editing existing location tags (for a variety of reasons). I am not sure if it began with the most recent Aperture update, or Mavericks, but the de-selection of any thumbnails on any click within the Map is most definitely new.
Here is a simple example of the round-trip scrolling behavior...
1. Double-Click the selected thumbnail. Note the vertical scroll position.
2. Double-Click to return to Browser view
3. The the selected thumbnail is no longer where it was in #1, but rather scrolled to be at the top.