Session support has died

As of this afternoon, any attempt to call a session-related function locks
up the httpd. I have rebuilt from scratch (PHP4.0RC2/OCI8, Apache 1.3.12).
No other changes were made on the server, so I am somewhat mystified. The
same happens with RC1. I observe the following symptoms:

1) Session files in /tmp are all zero-length (there is plenty of disk space
and permissions on the directory are normal)

2) The following sorts of log messages appear in great numbers in apache's
error_log:

string.c(1658) :  Freeing 0x0820F5CC (21 bytes), script=/www/live/about.php
./zend_execute.c(340) :  Freeing 0x0820BE54 (6 bytes),
script=/www/live/about.php
zend_variables.c(126) : Actual location (location was relayed)
./zend_execute.c(1591) :  Freeing 0x08203F64 (48 bytes),
script=/www/live/about.php
zend_hash.c(255) :  Freeing 0x08216B54 (43 bytes),
script=/www/live/firmlist.php
Last leak repeated 9 times
formatted_print.c(566) :  Freeing 0x08216B04 (30 bytes),
script=/www/live/firmlist.php
Last leak repeated 1 time
./zend_execute.c(1572) :  Freeing 0x0820FA64 (12 bytes),
script=/www/live/firmlist.php
Last leak repeated 3 times
./zend_execute.c(413) :  Freeing 0x0820F86C (12 bytes),
script=/www/live/firmlist.php
zend_execute_API.c(534) :  Freeing 0x08222504 (12 bytes),
script=/www/live/firmlist.php
Last leak repeated 3 times
zend_hash.c(425) :  Freeing 0x0820F644 (44 bytes),
script=/www/live/firmlist.php
./zend_execute.c(340) :  Freeing 0x082224CC (9 bytes),
script=/www/live/firmlist.php
zend_variables.c(126) : Actual location (location was relayed)
string.c(153) :  Freeing 0x08221004 (7 bytes), script=/www/live/firmlist.php
php_variables.c(163) :  Freeing 0x08204224 (12 bytes),
script=/www/live/firmlist.php
string.c(1658) :  Freeing 0x0820C904 (27 bytes),
script=/www/live/firmlist.php
./zend_execute.c(1591) :  Freeing 0x082018B4 (48 bytes),
script=/www/live/firmlist.php

3) Here's what lsof has to say, in case that's of any relevance:

timbuktu# lsof | grep tmp/sess
httpd-ora 25116    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25117    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25118    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25119    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25120    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25121    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
oracle    25122    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25123    root    4u   REG        8,1          0      16135
/tmp/sess_3c70db550a6943067bc92c4cebebedf4
oracle    25124    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
httpd-ora 25137    root    4u   REG        8,1          0      16274
/tmp/sess_3c70db550a6943067bc92c4cebebedf4 (deleted)
oracle    25202    root    4u   REG        8,1          0      16135
/tmp/sess_3c70db550a6943067bc92c4cebebedf4

Any ideas? I'm pretty well flummoxed.

miguel