On CVS tip:

$ postgres --single -Ddata postgres

PostgreSQL stand-alone backend 8.2devel
Segmentation fault (core dumped)

$ gdb -c core.18119
(gdb) bt
#0 pgstat_report_activity (cmd_str=0x67d25e "<IDLE>") at pgstat.c:1484
1484 beentry->st_changecount++;
(gdb) bt
#0 pgstat_report_activity (cmd_str=0x67d25e "<IDLE>") at pgstat.c:1484
#1 0x000000000056db8c in PostgresMain (argc=1, argv=0x8657d8,
username=0x867030 "qqzhou") at postgres.c:3132
#2 0x000000000050c918 in main (argc=4, argv=0x8657d0) at main.c:372
(gdb) p beentry
$1 = (volatile PgBackendStatus *) 0x0

Ooops, guess we forget to handle the single user mode in "current-status
information in shared memory" patch ...

Regards,
Qingqing