Changing FileSize in Rename Operation

Hi,

In my mini-filter in the set information callback of rename type I change the file size.
e.g. Rename A.txt to B.txt, I read all the contents of A.txt and then put some additional data in B.txt + contents of A.txt read previously. I do all the reads and writes in non-cached manner and also do not update the byteoffset.

This increase in size of B.txt is triggering a non cached write. What is the reason for this?

Thanks in Advance.
Mahesh