All ISO files from Microsoft shows CRC32 FFFFFFFF (0xffffffff)

Playing with Freeware Hash & CRC I noticed that CRC32 for all ISO files that comes from Microsoft (MSDN and Technet) are the same – FFFF FFFF. At first I thought that there is some bug in CRC implementation. But after taking look at the file ending in hex, I found, that all files have something like this at the end:
ExclCRC 0'm#AutoCRC _Ų¢v

Also, Google search revealed that many MS ISO files have check-sum of 0xFFFFFFFF. There is something to do with AutoCRC and ExclCRC… Go figure!