FreeBSD 6.1: open(/dev/lpt0, O_WRONLY) hangs up

[george+freebsd at m5p.com]

Print jobs get into my print queu, but they don't get out.  So I started
debugging lpd.  After a lot of screwing around, I discovered that the
program was hanging up on line 1875 of printjob.c:

        pfd = open(pp->lp, pp->rw ? O_RDWR : O_WRONLY);

pp->lp is "/dev/lpt0"
pp->rw is 0

So then I returned to my shell prompt and typed in:

cat /dev/null >/dev/lpt0

and that hung up uninterruptibly.  What's going on?

FreeBSD 6.1-RELEASE, unmodified generic kernel.  All this worked normally
under 5.3, though that needed 'hw.intr_storm_threshold="2000"'.