Border does not need to cast shadows by itself, it's already handled as part of the box. For example, a div with a dotted border casts a rectangular shadow, without extra dots surrounding the rectangle. This behavior was first introduced in http://trac.webkit.org/changeset/34763.
And due to http://trac.webkit.org/changeset/47103, too.
Created attachment 64430 [details] Patch
Comment on attachment 64430 [details] Patch Nice step forward to bug 44025!
Comment on attachment 64430 [details] Patch Clearing flags on attachment: 64430 Committed r65392: <http://trac.webkit.org/changeset/65392>
All reviewed patches have been landed. Closing bug.