I'm having similar problem as Bug#18044.

 Here is a backtrace of my Apache Core file. 
I had originally reported to bugzilla.apache.org, but they referred the
backtrace to php.

Basically, the symptoms are the same as mgriego's. Seg Faults occur after
about a day or sometimes even several hours of running apache w/PHP
4.2.2 parsed-pages.

Here are my build specs:

I am using the following components with Apache Web Server 1.3.26 on a
Solaris 
9 platform:
openssl-engine-0.9.6d
mm-1.1.3
mod_ssl-2.8.10-1.3.26
php-4.2.2

Configur Options Used:
./configure --with-mysql --with-apxs=/usr/local/apache/bin/apxs --with-ftp --with-oci8 --with-
mm=/usr/local/mm --with-mcrypt=/usr/local/bin --enable-trans-sid --enable-debug


I will also include backtrace originally given to apache dudes:
Output from gdb backtrace:

#0  ps_mm_destroy (data=0x1091b8) at mod_mm.c:241
#1  0xfeca8348 in zm_shutdown_ps_mm (type=0, module_number=10) at
mod_mm.c:293
#2  0xfec56eac in module_destructor (module=0x113650) at
zend_API.c:1127
#3  0xfec59014 in zend_hash_destroy (ht=0xfed6ee7c) at zend_hash.c:541
#4  0xfec53d98 in zend_shutdown () at zend.c:490
#5  0xfec6289c in php_module_shutdown () at main.c:1050
#6  0xfec6284c in php_module_shutdown_wrapper (sapi_globals=0x0) at
main.c:1027
#7  0xfec5fd48 in apache_php_module_shutdown_wrapper () at
mod_php4.c:795
#8  0x1a9f0 in run_cleanups ()
#9  0x1825c in ap_clear_pool ()
#10 0x182f0 in ap_destroy_pool ()
#11 0x18244 in ap_clear_pool ()
#12 0x182f0 in ap_destroy_pool ()
#13 0x2e9c8 in clean_parent_exit ()
#14 0x32a7c in standalone_main ()
#15 0x33278 in main ()

I would like to further investigation of this problem. Seems maybe to me
mm-releted to me at this point. I too am using sessions
(session_start())

If more tracing is needed, please reply. I just recently recompiled PHP to enable debug. I am currently running another GDB trace. I will try to give you another backtrace when the problem occurs again. In the meantime, maybe something can be seen with the one included here.

THanks
-George