I guess this affects ALL places using rfc822_parse_adrlist() and not duplicating the passed data. I'll look into this. Maybe you could provide more tests those functions that use this c-client func? :)

Can't reproduce with PHP_5_2 branch. Looks like someone didn't bother merging some fixes from that branch to HEAD/PHP_5_3..

Looks like this only happens with imap_mail_compose() with uses rfc822_parse_adrlist(). imap_mail() with uses that function through _php_imap_mail() is not affected. New test:

--TEST--
imap_rfc822_parse_adrlist() adding NUL byte to argument.
--SKIPIF--
<?php if (!extension_exists('imap')) echo 'skip IMAP extension not installed'; ?>
--FILE--
<?php

$address = 'John Doe <john@example.com>';
imap_rfc822_parse_adrlist($address, null);
echo $address;

echo "\n";
$envelope = array('return_path' => 'John Doe <john@example.com>',
                  'from'        => 'John Doe <john@example.com>',
                  'reply_to'    => 'John Doe <john@example.com>',
                  'to'          => 'John Doe <john@example.com>',
                  'cc'          => 'John Doe <john@example.com>',
                  'bcc'         => 'John Doe <john@example.com>');
imap_mail_compose($envelope, array(1 => array()));
var_export($envelope);

echo "\n";
$to  = 'John Doe <john@example.com>';
$cc  = 'John Doe <john@example.com>';
$bcc = 'John Doe <john@example.com>';
imap_mail($to, 'Subject', 'Body', '', $cc, $bcc);
echo $to;
echo "\n";
echo $cc;
echo "\n";
echo $bcc;

?>
--EXPECT--
John Doe <john@example.com>
array (
  'return_path' => 'John Doe <john@example.com>',
  'from' => 'John Doe <john@example.com>',
  'reply_to' => 'John Doe <john@example.com>',
  'to' => 'John Doe <john@example.com>',
  'cc' => 'John Doe <john@example.com>',
  'bcc' => 'John Doe <john@example.com>',
)
John Doe <john@example.com>
John Doe <john@example.com>
John Doe <john@example.com>

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

And thanks for the tests. :)