repeatable ufs2 softupdate panic ffs_alloccg: map corrupted

I got a couple of kernel crashes this morning when amanda tried to
allocate disk space.  I guessed which structure this was writing to,
unounted it and did a fsck -f -y on it.  Remounted it and all is happy
now.  It corrected three block counts that where off.  This was in 5.1
-current less than a week old

Shouldnt it have forced a regular fsck at boot time on its own?  Or how
come the background fsck didnt complain about it?

panic: ffs_alloccg: map corrupted
panic messages:
---
dmesg: kvm_read: 
---

warning: failed to read linker file data at 0xcc02aa00

#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
240             dumping++;
(kgdb) where
#0  doadump () at /usr/src/sys/kern/kern_shutdown.c:240
#1  0xc030bd6b in boot (howto=260) at
/usr/src/sys/kern/kern_shutdown.c:372
#2  0xc030c176 in panic () at /usr/src/sys/kern/kern_shutdown.c:550
#3  0xc0352a71 in bremfreel (bp=0xd82a6628) at
/usr/src/sys/kern/vfs_bio.c:644
#4  0xc0352945 in bremfree (bp=0x0) at /usr/src/sys/kern/vfs_bio.c:626
#5  0xc035c921 in vop_stdfsync (ap=0xe6d867c0) at
/usr/src/sys/kern/vfs_default.c:740
#6  0xc02d1870 in spec_fsync (ap=0xe6d867c0) at
/usr/src/sys/fs/specfs/spec_vnops.c:417
#7  0xc02d0b48 in spec_vnoperate (ap=0x0) at
/usr/src/sys/fs/specfs/spec_vnops.c:122
#8  0xc0428417 in ffs_sync (mp=0xcbda6400, waitfor=2, cred=0xc6752e80,
td=0xc05a3960) at vnode_if.h:627
#9  0xc0368c2b in sync (td=0xc05a3960, uap=0x0) at
/usr/src/sys/kern/vfs_syscalls.c:142
#10 0xc030b8bf in boot (howto=256) at
/usr/src/sys/kern/kern_shutdown.c:281
#11 0xc030c176 in panic () at /usr/src/sys/kern/kern_shutdown.c:550
#12 0xc0410e41 in ffs_mapsearch (fs=0xcc013800, cgp=0xdf150000,
bpref=8589934592, allocsiz=8)
    at /usr/src/sys/ufs/ffs/ffs_alloc.c:2041
#13 0xc040f414 in ffs_alloccgblk (ip=0xcbdb06c0, bp=0xd82a6628,
bpref=120663592) at /usr/src/sys/ufs/ffs/ffs_alloc.c:1405
#14 0xc040f043 in ffs_alloccg (ip=0xcbdb06c0, cg=1283, bpref=120663592,
size=16384) at /usr/src/sys/ufs/ffs/ffs_alloc.c:1302
#15 0xc040e9f7 in ffs_hashalloc (ip=0xcbdb06c0, cg=1283, pref=0,
size=16384, allocator=0xc040eee0 <ffs_alloccg>)
    at /usr/src/sys/ufs/ffs/ffs_alloc.c:1155
#16 0xc040c8d7 in ffs_alloc (ip=0xcbdb06c0, lbn=274445, bpref=120663592,
size=16384, cred=0xcc2e9280, bnp=0xe6d86a58)
    at /usr/src/sys/ufs/ffs/ffs_alloc.c:157
#17 0xc04122c0 in ffs_balloc_ufs1 (vp=0xcb93e7fc, startoffset=0,
size=16384, cred=0xcc2e9280, flags=2130706432, bpp=0xe6d86b9c)
    at /usr/src/sys/ufs/ffs/ffs_balloc.c:311
#18 0xc0429b67 in ffs_write (ap=0xe6d86be0) at
/usr/src/sys/ufs/ffs/ffs_vnops.c:698
#19 0xc0371183 in vn_write (fp=0xcc42bcc0, uio=0xe6d86c7c,
active_cred=0xcc2e9280, flags=0, td=0xcb907e40) at vnode_if.h:432
#20 0xc0333ce8 in dofilewrite (td=0xcb907e40, fp=0xcc42bcc0, fd=0,
buf=0x50238000, nbyte=0, offset=0, flags=0)
    at /usr/src/sys/sys/file.h:249
#21 0xc0333b1e in write (td=0xcb907e40, uap=0xe6d86d10) at
/usr/src/sys/kern/sys_generic.c:330
#22 0xc0492253 in syscall (frame=
      {tf_fs = 47, tf_es = 47, tf_ds = -1078001617, tf_edi = 240, tf_esi
      = 4, tf_ebp = -1077938056, tf_isp = -422023820, tf_ebx =
      1208604828, tf_edx = 240, tf_ecx = 32768, tf_eax = 4, tf_trapno =
      22, tf_err = 2, tf_eip = 1209550783, tf_cs = 31, tf_eflags = 514,
      tf_esp = -1077938116, tf_ss = 47}) at
      /usr/src/sys/i386/i386/trap.c:1008
#23 0xc047988d in Xint0x80_syscall () at {standard input}:145
---Can't read userspace from dump, or kernel process---