Learned something about SCCM OSD today, just not sure what!

I was attempting to do a build of Windows 7 and I was using an x64 boot image on an x86 build. During the image build process it actually downloaded PE put it on disc, and rebooted similar to a refresh scenario. The strange thing was it still formatted. After the second reboot (after it copied PE) it couldn’t find the boot record. I am not sure what happened yet but it would appear that you should match your boot image to your OS. Now this may be a Windows 7 anomaly so YMMV. If anyone else has some insight on what I saw speak up and I will try to repost with more detailed information.