Examination of the source code for the button found a new address encoded for "Share this".
Hence place the new address in IE's Safety-Internet Options-Security-Restricted Sites list, to wit add this new address:
http://w.sharethis.com
This removes the button from the screen and the problems with this site.
As stated previously, this button and script interferred with the back function not only on this site but on other later visited sites and it encoded a very invasive form of tracking, even after selecting "opt out" per it's privacy statement.
Edited by Geomean, 04 February 2012 - 12:27 PM.