CSV ajax download has cryptic filename

#1

Here is my response in a formwidget request controller:

...
$headers = array(
        'Cache-Control'       => 'must-revalidate, post-check=0, pre-check=0',
        'Content-type'        => 'text/csv; charset=UTF-8',
        'Content-Disposition' => "attachment; filename=" . $fileName . '"',
        'Expires'             => '0',
        'Pragma'              => 'public',
    );

    return Response::download($filePath, $fileName, $headers);
...

I send the request via data-request attribute, as described in here:
Handle File Downloads using the AJAX Framework - Updates and Announcements - October Talk (octobercms.com)

<button 
        id="birthday-subscription-export-csv"
        type="button"
        data-id="<?= $id; ?>"
        onclick="$(this).data('request-data', { id: $(this).data('id') })"
        data-request="onExportCsv"
        data-request-download
        data-browser-target="_blank"
        data-load-indicator="Downloading CSV..." class="btn btn-primary"
>
        Export CSV
</button>

Everything works fine, but the filenames keep being cryptic like T0JkSNIB.csv or 3SSRIYGB.csv. The $fileName would be a nice and readable string.

I could not find an answer to this anywhere else.