When you go to http://googleapp.ccsd.net/search?q=aup&btnG=Search&client=ccsd&proxystylesheet=ccsd&output=xml_no_dtd&site=CCSD and click on a PDF file (the first one in the list will do), while on the latest nightly (r25261), you get double vertical scroll bars. One from the previous page, and the other (inside) one is for the PDF itself.
Created attachment 16139 [details]
screenshot of issue
Confirmed with r25262. This regressed with <http://trac.webkit.org/projects/webkit/changeset/25142>.
I doubt this is a site specific issue. This seems to happen on any page that links to a PDF. Such as a Google result page: http://www.google.com/search?hl=en&q=filetype%3Apdf&btnG=Search
working on this...
Committed revision 25307