AtomPub client update fails

I've been trying to update an entry using an AtomPub client - I'm using http://search.cpan.org/~miyagawa/XML-Atom/ . Reads work fine, but with updates I get:

Error on PUT http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com/cgi-bin/mt/mt-atom.cgi/1.0/blog_id=1/entry_id=1: 500 Can't call method "body" on an undefined value at lib/MT/AtomServer.pm line 655.

The error is the same in MT 4.2 and 4.3 and I have repeated it in a couple of different environments.

Here's my test code, which updates the 1st blog's 1st entry:

#!/usr/bin/perl -w

use strict;

use XML::Atom::Client;

use XML::Atom::Entry;

my $username = 'xxxxx';

my $password = 'xxxxx';	# Web services password from MT - edit profile

my $EditURI = 'http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com/cgi-bin/mt/mt-atom.cgi/1.0/blog_id=1/entry_id=1';

/

my $api = XML::Atom::Client->new;

$api->username($username);

$api->password($password);

my $entry = $api->getEntry($EditURI);

unless (defined $entry) {

	print $api->errstr, "\n";

	exit;

}

my $title = $entry->title();

my $body = $entry->content()->body();

print 'Title:   ', $title, "\n";

print 'Old Content: ', $body, "\n";

my ($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) = localtime time;

$body .= sprintf "<br/>Updated by AtomPub %4d-%02d-%02d %02d:%02d:%02d<br/>", $year+1900, $mon+1, $mday, $hour, $min, $sec;

print 'New Content: ', $body, "\n";

$entry->title($title);

#$entry->content()->body($body);

$entry->content($body);

my $res = $api->updateEntry($EditURI, $entry);

unless (defined $res) {

	print $api->errstr, "\n";

	exit;

}

print "Program terminated normally\n";

Here's what I'm sending through the client:

<?xml version="1.0" encoding="utf-8"?>
<entry xmlns="http://www.w3.org/2005/Atom">
  <summary/>
  <author>
    <name>Administrator</name>
    <email>rob@xxxx.xxx</email>
  </author>
  <published>2009-09-02T17:27:11+00:00</published>
  <updated>2009-09-02T17:28:28+00:00</updated>
  <link rel="alternate" href="http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com/my_first_blog/2009/09/i-just-finished-installing-movable-type-4.html" type="text/html"/>
  <id>tag:ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com,2009:/my_first_blog//1.1</id>
  <edited xmlns="http://www.w3.org/2007/app">2009-09-02T17:28:28+00:00</edited>
  <link rel="edit" href="http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com/cgi-bin/mt/mt-atom.cgi/1.0/blog_id=1/entry_id=1" title="I just finished installing Movable Type 4!" type="application/atom+xml"/>
  <link rel="replies" href="http://ec2-xxx-xxx-xxx-xxx.compute-1.amazonaws.com/cgi-bin/mt/mt-atom.cgi/comments/blog_id=1/entry_id=1" type="application/atom+xml"/>
  <title>I just finished installing Movable Type 4!</title>
  <content type="xhtml">
    <div xmlns="http://www.w3.org/1999/xhtml">Welcome to my new blog powered by Movable Type. This is the first post on my blog and was created for me automatically when I finished the installation process. But that is ok, because I will soon be creating posts of my own!<br/><br/>This time I installed it on a 2G bootable EBS volume.<br/><br/>Updated by AtomPub 2009-09-02 18:41:34<br/></div>
  </content>
</entry>

Is this something wrong with my AtomPub client?