InUseCount of CIM_DataFile does not work.

Hi,

The InUseCount of CIM_DataFile always seems to return a value of null. I
read elsewhere on the web too that this is an unreliable field. Why is that
so?
I have opened a text file using notepad two times and i expect the
InUseCount for that file to be shown as '2' - Am I missing something here?

OS: Windows XP, SP2.

Query used against CIMv2 in wbemtest:

select * from cim_datafile where name='c:\\temp\\issues.txt'

(where issues.txt was opened twice using notepad)

Or, is my understanding of this variable totally wrong?

TIA
Sriram