Starting from PHP4 I keep finding some running httpd processes. I attach to such process with gdb and always find it in chunk_free.
glibc is 2.1.2
gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)
Relevant (I think) config options:
httpd.conf - MaxRequestsPerChild 50 (trying to diagnose memory problems)
php.ini - memory_limit = 8M

./configure --enable-debug=no --enable-memory-limit --with-apxs=/usr/local/apache/bin/apxs --enable-versioning --with-mysql --with-gd --with-imap=/usr/local/

Backtrace:
#0  0x400f8763 in chunk_free (ar_ptr=0x4018c780, p=0x81f4158) at malloc.c:3065
#1  0x400f84c5 in __libc_free (mem=0x81f45d0) at malloc.c:2967
#2  0x401d74a8 in _efree (ptr=0x81f45dc) at zend_alloc.c:238
#3  0x401f38cb in zend_hash_destroy (ht=0x82a37c0) at zend_hash.c:567
#4  0x401ea019 in destroy_zend_class (ce=0x82a37a8) at zend_opcode.c:128
#5  0x401f3a0d in zend_hash_apply_deleter (ht=0x80ea388, p=0x8226ce8) at zend_hash.c:619
#6  0x401f3b68 in zend_hash_apply (ht=0x80ea388, apply_func=0x401e806c <is_not_internal_class>)
    at zend_hash.c:693
#7  0x401e8344 in shutdown_executor () at zend_execute_API.c:177
#8  0x401f00f6 in zend_deactivate () at zend.c:525
#9  0x4020098a in php_request_shutdown (dummy=0x0) at main.c:688
#10 0x401fe664 in php_apache_request_shutdown (dummy=0x0) at mod_php4.c:288
#11 0x80715fe in run_cleanups ()
#12 0x806fe2d in ap_clear_pool ()
#13 0x806fea1 in ap_destroy_pool ()
#14 0x806fe1c in ap_clear_pool ()
#15 0x807f5ef in child_main ()
#16 0x807fc3c in make_child ()
#17 0x807ffb6 in perform_idle_server_maintenance ()
#18 0x80804e5 in standalone_main ()
#19 0x8080aa3 in main ()
#20 0x400b71fb in __libc_start_main (main=0x808075c <main>, argc=1, argv=0xbffffe04,
    init=0x804ee50 <_init>, fini=0x80b4e40 <_fini>, rtld_fini=0x4000a610 <_dl_fini>,
    stack_end=0xbffffdfc) at ../sysdeps/generic/libc-start.c:90