QuerySetCell changes numeric value

I have a query that is a Q of Q from a cfdirectory, getting a list of image files

<!--- Query the Query --->
<cfquery name="application.listimages" dbtype="query">
SELECT NAME, DATELASTMODIFIED, SIZE as filesize
FROM application.imagedir
ORDER by NAME
</cfquery>

Works fine.

What I want to do, before I output my xml for the gallery i am using, is to format the filesize value in the query.

Using 'querySetCell()' , I am having results I cannot explain.

<cfloop query="application.listImages">
<cfset sizevaltemp = querySetCell(application.listImages, 'filesize', '#numberFormat(filesize, ',')#', #rowID#)>
</cfloop>

If I do a cfdump for "numberformat(filesize, ',')", I get the correct, formatted number.
But if I dump out the query after this point, the number inserted is a different, negative value.

Is there something strange about querysetcell() and numeric values?
How can I replace the value of this existing query object row by row in my cfloop?