I was deleting (expunging) a large email from my IMAP mailbox, and got
the following panic:

ffs_fsync: dirty: tag 1 type VREG, usecount 1, writecount 1, refcount 3,
        tag VT_UFS, ino 2089006, on dev 4, 0 flags 0x18, effnlink 1, nlink 1
        mode 0100640, owner 500, group 0, size 22250907 lock type vnlock: EXCL (count 1) by pid 305
panic: softdep_deallocate_dependencies: dangling deps
Stopped in pid 305 (imapd) at   cpu_Debugger+0x4:        ret      zero,(ra)
db> t
cpu_Debugger() at cpu_Debugger+0x4
panic() at panic+0xf8
softdep_deallocate_dependencies() at
softdep_deallocate_dependencies+0x28
brelse() at brelse+0x170
ffs_indirtrunc() at ffs_indirtrunc+0x3e0
ffs_indirtrunc() at ffs_indirtrunc+0x2b4
ffs_truncate() at ffs_truncate+0x61c
VOP_TRUNCATE() at VOP_TRUNCATE+0x48
ufs_setattr() at ufs_setattr+0x244
VOP_SETATTR() at VOP_SETATTR+0x44
sys_ftruncate() at sys_ftruncate+0x128
syscall_plain() at syscall_plain+0x12c
XentSys() at XentSys+0x5c
--- syscall (198) ---
--- user mode ---
db>

After the dump and reboot, fsck said:
/dev/rwd0a: PARTIALLY TRUNCATED INODE I=2089006 (SALVAGED)
/dev/rwd0a: INCORRECT BLOCK COUNT I=2089006 (43520 should be 27344) (CORRECTED)

and my mailbox looks fine (whew!), with the large email deleted. As the
first few lines said, the mbox file was originally about 22 megs, and
now it's down to 13986553 bytes.

dumpfs /dev/rwd0a says (in part):
endian  little-endian
magic   11954   time    Thu Dec 28 13:12:38 2000
cylgrp  dynamic inodes  4.4BSD  fslevel 3       softdep enabled
nbfree  4224498 ndir    17483   nifree  2697922 nffree  103667
ncg     868     ncyl    27748   size    45034920        blocks  44666858
bsize   8192    shift   13      mask    0xffffe000
fsize   1024    shift   10      mask    0xfffffc00
frag    8       shift   3       fsbtodb 1
cpg     32      bpg     6492    fpg     51936   ipg     3264
minfree 5%      optim   time    maxcontig 8     maxbpg  2048
rotdelay 0ms    headswitch 0us  trackseek 0us   rps     120
ntrak   6       nsect   541     npsect  541     spc     3246
symlinklen 60   trackskew 0     interleave 1    contigsumsize 8
maxfilesize 0x0000400801017fff
nindir  2048    inopb   64      nspf    2
sblkno  16      cblkno  24      iblkno  32      dblkno  440
sbsize  3072    cgsize  8192    offset  272     mask    0xfffffff8
csaddr  440     cssize  14336   shift   9       mask    0xfffffe00
cgrotor 686     fmod    0       ronly   0       clean   0x02

and my kernel is NetBSD/alpha 1.5P, from December 27.
-- 
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 25 Y++ L+++ W- C++ T++ A+ E+ S++ V++ F- Q+++ P+ B+ PA+ PL++