First of all:
Best wishes to you all!

Now for the annoying stuff:

This bug seems similar to 8492.

Offending code, remove the /* */ and it core-dumps:
$xml_file='bla.xml';
if (!(list($xml_parser, $fp) = new_xml_parser($xml_file))) {
    die("could not open XML input");
}
print "<pre>";
while ($data = fread($fp, 4096)) {
/*	if (!xml_parse($xml_parser, $data, feof($fp))) {
	die(sprintf("<span style='color: red; font-weight: bold'>XML error: %s at line %d</span>\n",
		xml_error_string(xml_get_error_code($xml_parser)),
		xml_get_current_line_number($xml_parser)));
	}*/
	echo $data;
}
print "</pre>";
xml_parser_free($xml_parser);


Output BSDi gdb backtrace:

Program terminated with signal 11, Segmentation fault.
#0  0x48253c7b in zend_hash_exists (ht=0x816273c, arKey=0x8047d0c "\030}\004\b??\004\b\f\020\013\b$}\004\b1?\004\b\f?\n\b0}\004\b??\005\b\f?\n\bP}\004\b??\005\b",
    nKeyLength=134542129) at zend_hash.c:907
907             p = ht->arBuckets[nIndex];
(gdb) bt
#0  0x48253c7b in zend_hash_exists (ht=0x816273c, arKey=0x8047d0c "\030}\004\b??\004\b\f\020\013\b$}\004\b1?\004\b\f?\n\b0}\004\b??\005\b\f?\n\bP}\004\b??\005\b",
    nKeyLength=134542129) at zend_hash.c:907
#1  0x804f2bd in ap_clear_pool ()
#2  0x804f331 in ap_destroy_pool ()
#3  0x804f2ac in ap_clear_pool ()
#4  0x804f331 in ap_destroy_pool ()
#5  0x805ccf6 in clean_parent_exit ()
#6  0x805f6b3 in standalone_main ()
#7  0x805fb89 in main ()
#8  0x804ebb7 in __start ()

The PHP code did not modify since php 4.03pl1, but only started being troublesome, in version 4.04.

Other changes with the upgrade:
-- chrooted environment
-- apache 1.3.12 -> 1.3.14

I will go back to php4.03pl1 and report if that makes a difference.

Melvyn.