Sysinstall dying with 'BARF' error.

I've recently tried to boot the latest -current snapshot on a Compaq
V6107au.  Whilst it will actually boot (after I disable ACPI - which
is still better than 6.1 or 6.2 can manage), sysinstall then dies with
the error "BARF 170 <105>" just after it reports "probing devices" and
the system panics.

Looking at src/lib/libdisk/open_disk.c, about all this tells me is
that there was an unexpected 'i' in the GEOM config returned by
kern.geom.conftxt.  Can anyone offer any suggestions on how to
proceed.

-- 
Peter Jeremy