PHP segfaults if parent:: is used in a class that is
defined in a file other than the file in which its base class
is defined.

Example code:
*** one.php ***
<?
class a
{
        function g()
        {
                echo "x\n";
        }
}
?>

*** two.php ***
<?
require("one.php");
class b extends a
{
        function f()
        {
                parent::g();
        }
}
header("content-type: text/plain");
b::f();                                                                                                                                  
?>

(gdb) bt
#0  0x40226874 in execute (op_array=0x8119ba4) at zend_execute.c:1426
#1  0x40226f96 in execute (op_array=0x81135e4) at zend_execute.c:1544
#2  0x40237eab in zend_execute_scripts (type=8, file_count=3) at zend.c:752
#3  0x4024f89c in php_execute_script (primary_file=0xbffff644) at main.c:1206
#4  0x4024b105 in apache_php_module_main (r=0x80fb1a4, display_source_mode=0) at sapi_apache.c:89
#5  0x4024be20 in send_php (r=0x80fb1a4, display_source_mode=0, filename=0x80fbd54 "/home/blixen/carl/apache/htdocs/test/two.php")
    at mod_php4.c:536
#6  0x4024be65 in send_parsed_php (r=0x80fb1a4) at mod_php4.c:547
#7  0x8054973 in ap_invoke_handler ()
#8  0x8068bab in process_request_internal ()
#9  0x8068c20 in ap_process_request ()
#10 0x805ff7d in child_main ()
#11 0x80601e7 in make_child ()
#12 0x806029b in startup_children ()
#13 0x806090d in standalone_main ()
#14 0x806113b in main ()
#15 0x400c7a8e in __libc_start_main (main=0x8060da0 <main>, argc=1, argv=0xbffff924, init=0x804eb28 <_init>, fini=0x8096c90 <_fini>,
    rtld_fini=0x4000aa50 <_dl_fini>, stack_end=0xbffff91c) at ../sysdeps/generic/libc-start.c:92