unmount: dangling vnode on 5.3 (no vinum)

I have a machine which i have (oct 25) cvsup and moved to RELENG_5.
It was previously running 5.1.

The machine does not use vinum. I am using 'amd' automounter.
When a certain host becomes unavailable (that host is using 
nfsv2), automounter times it out. During the umount (sometimes? 
always? not sure),
i get: "unmount: dangling vnode" panic.

I have a vmcore from it, and a kernel.debug.

I'm a little confused on gdb, there is no -k switch anymore?
I'm very familiar with 4.x, less so with 5.x, how does one
do kernel debugging with gdb?
The handbook still says -k 
(http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-gdb.html)


Has anyone seen this? Is there a workaround?

FreeBSD labgw8.phaedrus.sandvine.com 5.3-STABLE FreeBSD 5.3-STABLE #15: Mon Oct 25 23:18:50 EDT 2004     don_at_cdata.sandvine.com:/d2/usr/obj/d2/usr/src/sys/CDATA  i386

The amd entry is:

mfg_cc_views    -type:=nfs;rfs:=/m;addopts:=vers=2,proto=udp \
                rhost:=mfgrembo.mfg.wtl.sandvine.com

that seems to trip this, but others may too, just that machine 
has been having some trouble.