X-Requested-With/HTTP_X_REQUESTED_WITH weird problem

if 'X-Requested-With' in request.META:
    request.META['HTTP_X_REQUESTED_WITH'] = request.META['X-Requested-With']

case 'X':
    if (header_equals ("X-Forwarded-For", header_x_forwarded_for, begin, header_len)) {
        ret = add_known_header (hdr, header_x_forwarded_for, val_offs, val_len);
    } else if (header_equals ("X-Forwarded-Host", header_x_forwarded_host, begin, header_len)) {
        ret = add_known_header (hdr, header_x_forwarded_host, val_offs, val_len);
    } else
        goto unknown;
    break;