lsof: can't read inpcb at 0x00000000

Trying to work through the hang problem that I've been experiencing with
v7.0, and keep adding new tools. Tom suggested lsof, and running it
against the postmaster shows the above 'error' .. once it happens, it
doesn't appear to go away. Last hang, had two of those errors ... don't
know if they mean anything or are related, but figured I'd ask:

pgsql% cat cores/lsof.4969
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
postgres 4969 pgsql cwd VDIR 13,131084 1024 2 /pgsql
postgres 4969 pgsql rtd VDIR 13,131072 512 2 /
postgres 4969 pgsql txt VREG 13,131084 4669590 103169 /pgsql/bin/postgres
postgres 4969 pgsql txt VREG 13,131076 76648 212707 /usr/libexec/ld-elf.so.1
postgres 4969 pgsql txt VREG 13,131076 11128 56672 /usr/lib/libdescrypt.so.2
postgres 4969 pgsql txt VREG 13,131076 118044 56673 /usr/lib/libm.so.2
postgres 4969 pgsql txt VREG 13,131076 148316 56532 /usr/lib/libreadline.so.4
postgres 4969 pgsql txt VREG 13,131076 251416 56674 /usr/lib/libncurses.so.5
postgres 4969 pgsql txt VREG 13,131076 550996 56746 /usr/lib/libc.so.4
postgres 4969 pgsql 0r VCHR 2,2 0t0 7967 /dev/null
postgres 4969 pgsql 1w VREG 13,131084 857139 761872 /pgsql/logs/postmaster.5432.4968
postgres 4969 pgsql 2w VREG 13,131084 857139 761872 /pgsql/logs/postmaster.5432.4968
postgres 4969 pgsql 3u IPv4 0xd462a720 0t0 TCP *:5432 (LISTEN)
postgres 4969 pgsql 4u unix 0xd44a7780 0t0 ->(none)
postgres 4969 pgsql 5u IPv4 0xd4631500 0t0 TCP pgsql.tht.net:5432->smaug.vex.net:61189 (ESTABLISHED)
postgres 4969 pgsql 6u IPv4 0t0 TCP can't read inpcb at 0x00000000
postgres 4969 pgsql 7u IPv4 0t0 TCP can't read inpcb at 0x00000000
postgres 4969 pgsql 8u IPv4 0xd46300c0 0t0 TCP pgsql.tht.net:1046->smaug.vex.net:auth (ESTABLISHED)