address this problem observed with sources' upas/fs
and nasty apple client:

acid: stk()
cistrstr(sub=0x2e359,s=0x0)+0x3c /sys/src/libc/port/cistrstr.c:16
searchMsg(m=0x37ee0,s=0x2e308)+0x515 /sys/src/cmd/ip/imap4d/search.c:105
searchUCmd(uids=0x1,tg=0x2e258,cmd=0x2e298)+0x99 /sys/src/cmd/ip/imap4d/imap4d.c:1086
uidCmd(tg=0x2e258,cmd=0x2e278)+0xb8 /sys/src/cmd/ip/imap4d/imap4d.c:1326
imap4(preauth=0x0)+0x15f /sys/src/cmd/ip/imap4d/imap4d.c:332
main(argv=0xdfffef8c,argc=0x0)+0x19c /sys/src/cmd/ip/imap4d/imap4d.c:281
_main+0x31 /sys/src/libc/386/main9.s:16
acid: lstk()

- erik