This can be reproduced useing the example from xml_set_object() function reference found here:
http://www.php.net/manual/en/function.xml-set-object.php

Here is the exact reproduce code:
-------------------------------------
<?php
class xml  {
   var $parser;

   function xml()
   {
       $this->parser = xml_parser_create();

       xml_set_object($this->parser, $this);
       xml_set_element_handler($this->parser, "tag_open", "tag_close");
       xml_set_character_data_handler($this->parser, "cdata");
   }

   function parse($data)
   {
       xml_parse($this->parser, $data);
   }

   function tag_open($parser, $tag, $attributes)
   {
       var_dump($parser, $tag, $attributes);
   }

   function cdata($parser, $cdata)
   {
       var_dump($parser, $cdata);
   }

   function tag_close($parser, $tag)
   {
       var_dump($parser, $tag);
   }

} // end of class xml

$xml_parser = new xml();
$xml_parser->parse("<A ID='hallo'>PHP</A>");

$xml_parser = new xml();
$xml_parser->parse("<A ID='hallo'>PHP</A>");
?>
-------------------------------------

The only modification in comparison with the given example in the manual is the second assignment of $xml_parser to a new object.

The result is:
-------------------------------------
resource(2) of type (xml) string(1) "A" array(1) { ["ID"]=>  string(5) "hallo" } resource(2) of type (xml) string(3) "PHP" resource(2) of type (xml) string(1) "A"
Warning: xml_parse() [function.xml-parse.html]: Unable to call handler tag_open() in /home/local/dev.kenashkov.com/XPATS/bug_test/t4.php on line 16

Warning: xml_parse() [function.xml-parse.html]: Unable to call handler cdata() in /home/local/dev.kenashkov.com/XPATS/bug_test/t4.php on line 16

Warning: xml_parse() [function.xml-parse.html]: Unable to call handler tag_close() in /home/local/dev.kenashkov.com/XPATS/bug_test/t4.php on line 16
-------------------------------------

It works as expected in PHP 5.1.4

The code produces the bug in PHP 4.4.2 with the following cofigure line:
-------------------------------------
'./configure' '--prefix=/web/php4.4.2' '--with-apxs2=/web/apache2-php4/bin/apxs' '--enable-bcmath=shared' '--with-bz2=shared' '--enable-calendar=shared' '--enable-ctype=shared' '--with-curl=shared' '--enable-dba=shared' '--enable-dbase=shared' '--enable-dbx=shared' '--enable-dio=shared' '--with-dom=shared' '--with-dom-xsl=shared' '--with-dom-xslt=shared' '--with-dom-exslt=shared' '--enable-exif=shared' '--with-fam=shared' '--enable-ftp=shared' '--with-gettext=shared' '--with-gmp=shared' '--with-iconv=shared' '--with-gd=shared' '--with-jpeg-dir' '--with-png-dir' '--with-xpm-dir' '--with-ttf' '--with-freetype-dir' '--enable-gd-native-ttf' '--with-ldap=shared' '--enable-mbstring=all' '--enable-mbstr-enc-trans' '--enable-mbregex' '--with-mime-magic=shared' '--with-mysql=/web/mysql-max-5.0.15-linux-i686-glibc23' '--with-ncurses=shared' '--with-openssl=shared' '--enable-overload=shared' '--enable-pcntl=shared' '--with-pgsql=shared' '--with-regex' '--enable-maintainer-zts' '--enable-sysvsem=shared' '--enable-sysvshm=shared' '--enable-sysvmsg=shared' '--enable-shmop=shared' '--enable-sockets=shared' '--enable-memory-limit' '--enable-wddx=shared' '--with-zlib=shared' '--with-mhash=shared' '--with-mcrypt=shared' '--enable-xslt=shared' '--with-xslt-sablot' '--with-mssql=shared' '--with-kerberos=shared' '--enable-yp' '--enable-fastcgi' '--with-oci8=/u01/app/oracle/product/10.1.0/Db_1'
-------------------------------------

We are sorry, but we can not support PHP 4 related problems anymore.
Momentum is gathering for PHP 6, and we think supporting PHP 4 will
lead to a waste of resources which we want to put into getting PHP 6
ready.