One of my machines crashed today, and something strange happened when
it rebooted:

Automatic boot in progress: starting file system checks.
/dev/rwd0a: 604 files, 11727 used, 2536 free (152 frags, 298 blocks, 1.1% fragmentation)
/dev/rwd0a: MARKING FILE SYSTEM CLEAN
/dev/rwd0e: 2932 files, 63372 used, 13309 free (861 frags, 1556 blocks, 1.1% fragmentation)
/dev/rwd0e: MARKING FILE SYSTEM CLEAN
/dev/wd0a: file system not clean; please fsck(8)

Why's mount complaining that the filesystem isn't clean when fsck just
marked it as clean?

After a clean shutdown and reboot, I still get:

Automatic boot in progress: starting file system checks.
/dev/rwd0a: 604 files, 11732 used, 2531 free (147 frags, 298 blocks, 1.0% fragmentation)
/dev/rwd0a: MARKING FILE SYSTEM CLEAN
/dev/rwd0e: file system is clean; not checking
/dev/wd0a: file system not clean; please fsck(8)

wd0a is the root partition, and wd0e is /usr, which does seem to get
marked as clean...

The system is an i386, September 23 kernel and userland:
NetBSD sloth.metonymy.com 1.2G NetBSD 1.2G (SLOTH) #121: Wed Sep 24 00:58:00 CDT 1997     khym@dahan.metonymy.com:/usr/src.local/sys/arch/i386/compile/SLOTH i386

Name: Dave Huang     |   Mammal, mammal / their names are called /
INet: khym@bga.com   |   they raise a paw / the bat, the cat /
FurryMUCK: Dahan     |   dolphin and dog / koala bear and hog -- TMBG
Dahan: Hani G Y+C 21 Y++ L+++ W- C++ T++ A+ E+ S++ V++ F- Q+++ P+ B+ PA+ PL++