Why does exportOptions.antiAliasing not affect output?

Does anyone know why his basic javascript always results in an anti-aliased export as PNG..

if ( app.documents.length > 0 ) {

var doc = app.activeDocument;

var exportOptions = new ExportOptionsPNG24();

var fileSpec = new File(doc.path + '/test1.png');

exportOptions.antiAliasing = false;

app.activeDocument.exportFile( fileSpec, ExportType.PNG24, exportOptions );

}

As you can see antiAliasing is set to false but the output is antialiased.  Is there a Preference or setting somewhere in Illustrator that is overriding this option?

Using: AI CC on a PC