Scriptaculous drag/scrollable div with prototype.js - only half functionality when wrapper div is centered on page

[user1234]

I have an image map located inside a div with fixed width and height.
This "map" div is located inside a wrapper div with fixed width and
height. Everything works fine if the wrapper is not centered, but
when you set the margins to auto on the wrapper the dragging
functionality of the "map" does not change position.

http://medusa.mcs.uvawise.edu/~mrc8b

Any ideas??