MdlWriteComplete and ByteOffset

Gentlefolk,

Long ago we had a thread http://www.osronline.com/showThread.cfm?link=80853 which discussed the MdlChain in MdlWriteComplete. The simple question is about the ByteOffset field of the MDL in this path - can the ByteOffset ever be non-zero here? If so, what would be the correct handling in a filter driver, for access to the data in pre-op?

The context here is that since Windows Server 2012 I have started to see, very rarely, non-zero values for the ByteOffset field of the MDL in the CopyWrite path.

Thanks in advance, Lyndon