This isn't the same thing, but it does indicate something strange is going on. Here's a log of one small test of the plugin...
(08/19/2011 02:58:23 PM) Searching posters for: American Beauty
(08/19/2011 02:58:23 PM) GET: http://www.amazon.com/exec/obidos/search-handle-url/index=dvd&field-keywords=American+Beauty
(08/19/2011 02:58:23 PM) Redirected to: http://www.amazon.com/s?ie=UTF8&rh=n%3A2625373011&page=1
(08/19/2011 02:58:25 PM) GET: http://ecx.images-amazon.com/images/I/51RfEhuJhRL._SL160_AA115_.jpg
(08/19/2011 02:58:25 PM) GET: http://ecx.images-amazon.com/images/I/51WhUN1HrQL._SL160_AA115_.jpg
(08/19/2011 02:58:25 PM) GET: http://ecx.images-amazon.com/images/I/51REtKhE6lL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51cCy815g0L._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51zwKX-l%2BmL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51aSjj01OhL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51rybFChmDL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51r94O3uxPL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/61%2BQW9cUvoL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/51C3FRMvmjL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/512F90yEqdL._SL160_AA115_.jpg
(08/19/2011 02:58:26 PM) GET: http://ecx.images-amazon.com/images/I/516CIDGMlPL._SL160_AA115_.jpg
(08/19/2011 02:58:48 PM) Searching posters for: American Beauty
(08/19/2011 02:58:48 PM) GET: http://www.amazon.com/exec/obidos/search-handle-url/index=dvd&field-keywords=American+Beauty
(08/19/2011 02:58:48 PM) Redirected to: http://www.amazon.com/s?ie=UTF8&rh=n%3A2625373011&field-keywords=American%20Beauty&page=1
(08/19/2011 02:58:51 PM) GET: http://ecx.images-amazon.com/images/I/41TP3QGXCQL._SL160_AA115_.jpg
(08/19/2011 02:58:51 PM) GET: http://ecx.images-amazon.com/images/I/41PBDmK%2BqzL._SL160_AA115_.jpg
(08/19/2011 02:58:51 PM) GET: http://ecx.images-amazon.com/images/I/61qqjXCmXGL._SL160_AA115_.jpg
(08/19/2011 02:58:51 PM) GET: http://ecx.images-amazon.com/images/I/51HmOJSsW0L._SL160_AA115_.jpg
(08/19/2011 02:58:52 PM) GET: http://ecx.images-amazon.com/images/I/41qKTjxUoPL._SL160_AA115_.jpg
(08/19/2011 02:58:52 PM) GET: http://ecx.images-amazon.com/images/I/512F3B158GL._SL160_AA115_.jpg
(08/19/2011 02:58:52 PM) GET: http://ecx.images-amazon.com/images/I/41KDN6AM2NL._SL160_AA115_.jpg
(08/19/2011 02:58:52 PM) GET: http://ecx.images-amazon.com/images/I/41RGTP1JK8L._SL160_AA115_.jpg
(08/19/2011 02:58:52 PM) GET: http://ecx.images-amazon.com/images/I/519YJSCQQYL._SL160_AA115_.jpg
(08/19/2011 02:58:53 PM) GET: http://ecx.images-amazon.com/images/I/51R%2BSuuTvhL._SL160_AA115_.jpg
(08/19/2011 02:58:53 PM) GET: http://ecx.images-amazon.com/images/I/41pooqak-XL._SL160_AA115_.jpg
(08/19/2011 02:58:53 PM) GET: http://ecx.images-amazon.com/images/I/51xi5tRWebL._SL160_AA115_.jpg
The first attempt returns a bunch of apparently random posters. The problem is obvious: The redirect drops the search term. The search result is, not surprisingly, "Showing 1 - 12 of 855,914 Results." I tried it again and it worked properly, "Showing 1 - 12 of 240 Results"—most of which were
American Beauty posters.
And, as these things often go, after having no difficulty producing this result with several different movies, I can no longer reproduce it.