Images dumped from tests which include scrollbars do not include those scrollbars in their output image. You can observe this by looking at some of the tests in the css2.1 directory.
Created attachment 80287 [details]
Comment on attachment 80287 [details]
OK, we always have to be special don't we!
Committed r76749: <http://trac.webkit.org/changeset/76749>