.htaccess:
php_flag register_globals off
php_value session.save_path _sessions

php-script:
<script language=php>
        session_start();
        session_decode('selfas|s:4:"5089";');
</script>

backtrace:
Program received signal SIGSEGV, Segmentation fault.
0x401b2817 in _efree () at zend_alloc.c:281
281     zend_alloc.c: No such file or directory.
(gdb) bt
#0  0x401b2817 in _efree () at zend_alloc.c:281
#1  0x4020ca1a in php_rshutdown_session_globals () at session.c:1282
#2  0x4020cafc in php_rshutdown_session () at session.c:1287
#3  0x401cb2cd in module_registry_cleanup () at zend_API.c:758
#4  0x401ce7fa in zend_hash_apply () at zend_hash.c:639
#5  0x401ca6e9 in zend_deactivate_modules () at zend.c:253
#6  0x401da611 in php_request_shutdown () at main.c:581
#7  0x401d7f4b in php_apache_request_shutdown (dummy=0x0) at mod_php4.c:301
#8  0x80513f1 in run_cleanups ()
#9  0x804f963 in ap_clear_pool ()
#10 0x804f9e7 in ap_destroy_pool ()
#11 0x8060a83 in child_main ()
#12 0x8060be5 in make_child ()
#13 0x8060d66 in startup_children ()
#14 0x80613dd in standalone_main ()
#15 0x8061c0c in main ()
#16 0x400c5a8e in __libc_start_main () at ../sysdeps/generic/libc-start.c:93


Also tried:
1) giving session_decode() an empty string;
2) not calling session_start()