repeatable panic - ffs_blkfree: freeing free block

I'm getting a repeatable panic when trying to build openoffice with a
2005-01-12 kernel and world.  I manually fsck'ed the file system
immediately before the build.  The first panic happened during the
patching phase of the build.  I tried again and this time the panic
happened during configuration.

dev = da0s2a, block = 5090392, fs = /mnt
panic: ffs_blkfree: freeing free block
cpuid = 0
KDB: enter: panic
[thread pid 55 tid 100043 ]
Stopped at      kdb_enter+0x2c: leave   
db> tr
Tracing pid 55 tid 100043 td 0xc22fa450
kdb_enter(c0848a40,100,c22fa450,1361b80,4b5) at kdb_enter+0x2c
panic(c085f39d,c085f37d,c26cc280,4dac58,0) at panic+0x17f
ffs_blkfree(c2863800,c2987114,4dac58,0,4000) at ffs_blkfree+0x3a0
indir_trunc(136b060,0,0,c,0,e4d5bc4c) at indir_trunc+0x1bf
handle_workitem_freeblocks(0,0,0,1,0) at handle_workitem_freeblocks+0x2e6
process_worklist_item(41e7112d,0,0,c247d2bc,23) at process_worklist_item+0x1c0
softdep_process_worklist(0,29,41e7112d,1,0) at softdep_process_worklist+0x66
sched_sync(0,e4d5bd48,0,c0677b60,0) at sched_sync+0x3b2
fork_exit(c0677b60,0,e4d5bd48) at fork_exit+0x7e
fork_trampoline() at fork_trampoline+0x8
--- trap 0x1, eip = 0, esp = 0xe4d5bd7c, ebp = 0 ---

The kernel was built with INVARIANTS, WITNESS, and DEBUG_VFS_LOCKS.

I was able to get a crash dump from the first panic, so at least doadump
works for me.

After the crash, fsck reports some unexpected damage:
	PARTIALLY TRUNCATED INODE I=127552
but this inode doesn't seem to be associated with the block number in
the panic message.
% fsdb /dev/da0s2a
** /dev/da0s2a (NO WRITE)
Editing file system `/dev/da0s2a'
Last Mounted on /mnt
current inode: directory
I=2 MODE=40755 SIZE=512
        MTIME=Feb 14 11:55:43 2004 [0 nsec]
        CTIME=Feb 14 11:55:43 2004 [0 nsec]
        ATIME=Jan 13 16:15:58 2005 [0 nsec]
OWNER=root GRP=wheel LINKCNT=7 FLAGS=0 BLKCNT=4 GEN=53557245
fsdb (inum: 2)> inode 127552
current inode: regular file
I=127552 MODE=100644 SIZE=1932
        MTIME=Dec 22 07:47:38 2003 [0 nsec]
        CTIME=Dec 22 07:47:38 2003 [0 nsec]
        ATIME=Dec 22 07:57:30 2003 [0 nsec]
OWNER=root GRP=wheel LINKCNT=1 FLAGS=0 BLKCNT=4 GEN=1442a6af
fsdb (inum: 127552)> blocks
Blocks for inode 127552:
Direct blocks:
533086 (1 frag)

There are no snapshots present.