Greetings Wise Monks

I have created a simple test script for Excel::Template to experiment with formulae on one worksheet that reference cells values on another. The perl script and xml template are shown below

When I run the script I get the following error:

The script/template work correctly when all three rows are on a single worksheet.

Are cross-worksheet references beyond the scope of this module? Any advice greatly appreciated.

perl script

#!/usr/bin/perl
use strict;
use warnings;
use Excel::Template;
my $template = new Excel::Template();
$template->parse( 'test.xml' );
$template->write_file( 'test.xls' );
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xml template

<?xml version='1.0'?>
<!DOCTYPE spreadsheet>
<workbook>
  <worksheet name="Tab1">
    <row>
      <cell ref="one" type="number" text="1" />
      <cell ref="two" type="number" text="2" />
    </row>
  </worksheet>
  <worksheet name="Tab2">
    <row>
      <formula>=<backref ref="one" />+<backref ref="two" /></formula>
    </row>
  </worksheet>
</workbook>
[download]