modifying 9.9999 boot-com.iso using growisofs made init panic

[Andrew Cagney <andrew.cagney%gmail.com@localhost>]

I'm trying to automate a KVM install.

With 9.3 I've got two ISOs:
 boot-com.iso - unchanged
 install.iso - modified to contain a script that does a 1.5 style install
the framework boots the VM from the unmodified boot-com.iso, and then
sends commands to mount install.iso and run the script

With 9.9999.. because there's no install.iso (true?) I'm instead
modifying boot-com.iso (from nycdn).  My problem is that when the ISO
is modified using growisofs it seems to cause init to abort (no
message, kernel then panics).  The command I'm using is:
        growisofs -M $@.tmp -l \
                -input-charset utf-8 \
                -graft-points \
                /base.sh=$(KVM_NETBSD_BASE_DOMAIN).base.sh
if boot-com.iso isn't modified then, like for 9.3, it boots fine.

Is this expected?