this may be a bug.  I'll try and find some time to take a look.  

I'm not sure if it's a bug or not, but the behavior of the bulk build
scripts can be recovered by including the following in /etc/mk.conf:

USE_BULK_CACHE?=        yes

This variable is set by the bulk build scripts prior to running make.

The effect is to trigger a conditional that installs all the required
binary packages.  Without this, it appears that no BULK_PREREQ
packages are installed (I think I was wrong when I said earlier that
digest was installed).  

Two things to consider:

- should BULK_PREREQ packages be installed whenever the bulk-package
  target is invoked, not just when USE_BULK_CACHE is defined?

- should Packages.txt document this variable?

Cheers,
Brook