the httpd as well as the php cli crashes when pfpro is compiled in. 
Apache 2.0.35
php 4.2.0
Here's gdb output:

root@mars:~/php# gdb /opt/apache/bin/httpd 
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This GDB was configured as "i386-slackware-linux"...
(gdb) run -X
Starting program: /opt/apache/bin/httpd -X
[New Thread 1024 (LWP 5435)]

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1024 (LWP 5435)]
0x4037d7ab in ts_allocate_id (rsrc_id=0x404501b8, size=40, ctor=0x4030ba14 <php_pcre_init_globals>, 
    dtor=0x4030ba44 <php_pcre_shutdown_globals>) at TSRM.c:222
222                             if (p->count < id_count) {
(gdb) bt full
#0  0x4037d7ab in ts_allocate_id (rsrc_id=0x404501b8, size=40, ctor=0x4030ba14 <php_pcre_init_globals>, 
    dtor=0x4030ba44 <php_pcre_shutdown_globals>) at TSRM.c:222
        p = (tsrm_tls_entry *) 0x1bb
        size = 36
        ctor = 0x24 <__strtol_internal+36>
        dtor = 0x24 <__strtol_internal+36>
        i = 36
#1  0x4030baf2 in zm_startup_pcre (type=1, module_number=6, tsrm_ls=0x8149900) at php_pcre.c:97
        module_number = 6
        tsrm_ls = (void ***) 0x8149900
#2  0x402db090 in zend_startup_module (module=0x40437780) at zend_API.c:1007
        tsrm_ls = (void ***) 0x14
        module = (zend_module_entry *) 0x40437780
#3  0x402e54a0 in php_startup_extensions (ptr=0x404364fc, count=11) at main.c:831
        ptr = (zend_module_entry **) 0x40436510
        end = (zend_module_entry **) 0x40436528
#4  0x402ef3e3 in php_startup_internal_extensions () at internal_functions.c:66
No locals.
#5  0x402e5a87 in php_module_startup (sf=0x404314a0) at main.c:989
        zuf = {error_function = 0x402e42fc <php_error_cb>, printf_function = 0x402e3f88 <php_printf>, 
  write_function = 0x402e541c <php_body_write_wrapper>, fopen_function = 0x402e4824 <php_fopen_wrapper_for_zend>, 
  message_handler = 0x402e490c <php_message_handler_for_zend>, block_interruptions = 0, unblock_interruptions = 0, 
  get_configuration_directive = 0x402e48c0 <php_get_configuration_directive_for_zend>, ticks_function = 0x402ed28c <php_run_ticks>}
        zuv = {import_use_extension = 0x403d7dd0 ".php", import_use_extension_length = 1078189180}
        php_os = 0x403d7d34 "Linux"
        i = 1077768879
        tsrm_ls = (void ***) 0x8149900
#6  0x402e3203 in php_apache_server_startup (pconf=0x80b86a0, plog=0x80f0780, ptemp=0x80f2788, s=0x80bb3a8) at sapi_apache2.c:442
        pconf = (apr_pool_t *) 0x80b86a0
#7  0x807e974 in ap_run_post_config (pconf=0x80b86a0, plog=0x80f0780, ptemp=0x80f2788, s=0x80bb3a8) at config.c:129
        pHook = (ap_LINK_post_config_t *) 0x14
        n = 5
        rv = 36
#8  0x808365d in main (argc=2, argv=0xbffffad4) at main.c:569
        argc = 134984616
        argv = (char **) 0x80ad234
        c = 88 'X'
        configtestonly = 0
        confname = 0x80a5d50 "conf/httpd.conf"
        def_server_root = 0x80a5d60 "/opt/apache"
        process = (process_rec *) 0x80b6718
        server_conf = (server_rec *) 0x80bb3a8
        pglobal = (apr_pool_t *) 0x80b6698
        pconf = (apr_pool_t *) 0x80b86a0
        plog = (apr_pool_t *) 0x80f0780
        ptemp = (apr_pool_t *) 0x80f2788
        pcommands = (apr_pool_t *) 0x80ee778
        opt = (apr_getopt_t *) 0x80ee810
---Type <return> to continue, or q <return> to quit--- 
        rv = 20
        mod = (module **) 0x80ad234
        optarg = 0x0
#9  0x4017d2eb in __libc_start_main (main=0x8082fc8 <main>, argc=2, ubp_av=0xbffffad4, init=0x805ecec <_init>, 
    fini=0x809c94c <_fini>, rtld_fini=0x4000c130 <_dl_fini>, stack_end=0xbffffacc) at ../sysdeps/generic/libc-start.c:129
        ubp_av = (char **) 0xbffffad4
        fini = (void (*)()) 0x40015d64 <_dl_debug_mask>
        rtld_fini = (void (*)()) 0x814c9f0
        ubp_ev = (char **) 0x14
(gdb)