You got it:
http://rapidshare.com/files/43070135/Clip-002.mkv.html
It's 1 minute (in .mkv) cut with mkvtoolnix (23mb).
I didn't know if you wanted the raw x264 or not, but I did remove the audio to save on file size.
I would definitely like to know if CoreAVC is wrong. This is not the first x264 file I've come across that it reports as YUY2.
Edit: Hmm. The video renderer in MPC reports YV12.... that's odd.
I wonder which program is going wrong.