Hi,
Same Problem with KB2821895 for me on Win8 x86
I discovered it to be problematic when I ran cleanmgr.exe afterwards, which took nearly 2 hours under 100 % CPU Usage.
Thereafter got same problems with System File Checker reported by the others here.
Also strange:
After Update & running cleanmgr.exe, there is a huge "Reserve.tmp"-file in Windows/WinSxs, about 2 Gigs on my system, other folks in german forums report the same with different sizes from ca. 100 MB to > 3 Gigs.
Hey, I had that two hour clean disk session.. dropped c drive from 40gb to 30, then back up to 33 when it made that side by side reserve.tmp 3.0gb file Don't delete that , it will go away at the right time.
Here's an article on win Vista explaining sxs.. its roots are same on win 8 I think;
http://blogs.technet.com/b/askcore/archive/2008/09/17/what-is-the-winsxs-directory-in-windows-2008-and-windows-vista-and-why-is-it-so-large.aspx
I spot checked after DISM and all those files show up in sxs, and many in regular tree folders. But not all - at least one is actually newer than the kb article shows. Maybe that's because of DISM.
You know Microsoft will send out a fix for this, or patch/break/disable the sfc from checking those files :)
Lots of things need fixing I think in win8, too dang sensitive to too many things. Look in event logs
ApplicationResourceManagement lots have 100's and more errors there continuously without ever knowing.