It seems that after a while of server inactivity, the apache
processes go into a mode where they continue to just use cpu
- the processes become unseable for processing http requests
since they just stay in this state. A server restart is
needed to correct the problem. A process stack listing shows
the process to be within the PHP module at the time:

0x400c2248: chunk_free + 0x270 (404407f4, 8118740, 4042f0f3)
0x400c1fba: __cfree + 0xaa (8118740, 404407f4, 4043da80,
4042f0f3, 624407f4, 6e9f190) + 34
0x4037ebb0: zend_hash_del_key_or_index + 0x1d8 (8111048,
4042f0ea, 9, 8da99e0, 0, 404407f4) + 10
0x4037c0af: zend_unregister_functions + 0x67 (4043da14,
ffffffff, 0, 404407f4, 81329f8)
0x4037c1bb: module_destructor + 0x73 (8132a28, 404407f4,
4000ae60, bffffdc4)
0x4037ec24: zend_hash_destroy + 0x30 (40455760, 404407f4)
0x4037b2f5: zend_shutdown + 0x25 (404407f4)
0x4038a4de: php_module_shutdown + 0x32 (404407f4)
0x4038a4a5: php_module_shutdown_wrapper + 0x15 (40437840,
403887f8)
0x40388817: php_child_exit_handler + 0x1f (80d15b0, 8151c70,
18, 40437940)
0x0806fa61: ap_child_exit_modules + 0x49 (8151c70, 80d15b0)
0x080758d5: clean_child_exit + 0x1d (0)
0x08077587: just_die + 0x1f (a)
0x080775a9: usr1_handler + 0x15 (a, 0, 0, 2b, 2b, bffffdc4) + dc
0x40086c68: sigaction + 0x268 (8126e70, 81479d8, 814dfa8,
6c060002, 2000a0a, c65451e8) + 18
0x080788b7: child_main + 0x1b7 (b, b, 0)
0x08078ebc: make_child + 0x118 (80d15b0, b, 3a8ad8e0,
401581ec, 4053e480, 0) + a0
0x08079236: perform_idle_server_maintenance + 0x2b2
(401581ec, ffffffff, 0, d, 0)
0x08079765: standalone_main + 0x355 (2, bffffdc4, bffffdc4,
40013ed0, 8049c54, 80cc6a4) + 30
0x08079d33: main + 0x357 (2, bffffdc4, bffffdd0, 40013868,
2, 8050600)
0x400809cb: __libc_start_main + 0xff (80799dc, 2, bffffdc4,
804fc60, 80b127c, 4000ae60) + 40000248


PHP configuration options listed below:
./configure --prefix=/usr
--with-apxs=/usr/sbin/httpd/bin/apxs
--with-config-file-path=/etc/httpd --enable-safe-mode
--with-exec-dir=/usr/sbin --with-system-regex
--disable-debug --with-zlib --with-dbdm --with-db2
--enable-debugger --enable-magic-quotes --enable-track-vars
--enable-sysvsem --enable-sysvshm --enable-track-vars
--with-xml --with-ftp --with-pgsql
--with-cybercash=/usr/src/cybercash/mck-3.3.0-i586-pc-linux-gnulibc2.1

glibc version is 2.1.3
php module was compiled with egcs-2.91.66
apache version is 1.3.14
kernel version 2.2.14

We also experienced this problem with PHP version 4.0.2.
After upgrading to the latest PHP, is seems that the problem
is occuring less frequently.