ExportOptionsTIFF not listening to my instructions!

I have discovered yet another inconvenience, and I hope someone may tell me what I am doing wrong.

Using the export TIFF command from an Illustrator document, I am hoping to produce a .tif with 600dpi.

#target illustrator-19

function test(){

    if(app.documents.length == 0){

        return;

    }

    var doc = app.activeDocument;

    var dest = Folder.selectDialog("Choose Folder.");

    if(dest != null){

        var opts = new ExportOptionsTIFF();

        opts.resolution = 600;

        var destFile = File(dest + "/" + "TestFile.tif");

        doc.exportFile(destFile, ExportType.TIFF, opts);

        alert("Successfully exported '" + destFile.displayName + "'.\nNow, check out that resolution...");

    }

}

test();

What I have found is that the script ignores my opts.resolution property and just uses the last resolution that was manually set through the File > Export / TIFF format dialog.
I am expecting new ExportOptionsTIFF(); to set the resolution, but it simply taunts me.
Is there anything wrong with my code?