As found out in discussions with Microsoft engineers at an interop event, when a client requests setting timestamps on a file to -1 or -2 this requests special behaviour from the server on the filehandle. -1 disable timestamp updates on subsequent IO operations on the file, -2 restores it. Link to MS doc to follow.
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/content/wdm/ns-wdm-_file_basic_information