panic: ffs_blkfree: freeing free block

Hello!

After suffering through

 http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/72451

and experiencing occasional ufs2 panics (rather than the usual system hangs), 
we recreated the troublesome partition as ufs1 without softupdates, with 
other newfs parameters being default.

We also set the mpsafenet and mpsafevm to 0, as it seemed to have helped 
increase the system's uptime in the past.

Under the load, the system eventually paniced with: 'ffs_blkfree: freeing free 
block'. The stack was:

 ffs_blkfree+0x433
 ffs_indirtrunc+0x37c
 ffs_indirtrunc+0x33c
 ffs_truncate+0xd24
 ufs_inactive+0x1d7
 vput+0x113
 kern_unlink+0x129
 unlink+0x3e

The machine runs fresh amd64-current on a single Opteron in a dual capable 
Tyan K8W motherboard. The troublesome harddrive is connected directly to the 
on-board SATA connector at SATA150 speed. We went through two drives, two 
SATA cables, already, and tried other on-board SATA connectors.

Is this panic just as likely to hit us if we go back to RELENG_5? Could the 
bug be stemming from some unsafeness in ata's reset/reinit code -- testing 
these must be painfully difficult, I understand.

Thanks!

 -mi