inset box-shadow displays wrong

Inset box-shadow are displayed wrong
I attach a screenshot of the problem the element is a div with fixed height and width and with this css:
 border: 1px solid red;
 position:absolute;
 border-radius: 5px;
 box-shadow: inset 0 0 3px red;
 background-color: rgba(255, 0, 0, 0.13);
 z-index: 10;
As you can see the inset box shadow is displayed wrong

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: libwebkitgtk-3.0-0 1.9.2-1ubuntu4
ProcVersionSignature: Ubuntu 3.5.0-15.23-generic 3.5.4
Uname: Linux 3.5.0-15-generic x86_64
ApportVersion: 2.5.2-0ubuntu4
Architecture: amd64
Date: Wed Sep 26 15:05:55 2012
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Beta amd64 (20120922)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: webkit
UpgradeStatus: No upgrade log present (probably fresh install)