Poudriere bulk "Deleting foo-1.2.3.pkg: no longer needed"

We use a staged approach to building packages with poudriere, with
several "bulk" commands, because some ports we rarely need take an
incredibly long time to build.  (Mainly languages, like rust, clang,
and gcc.)

Recently, each run of "poudriere bulk -f somefile.ports" generates
many lines of the form:

[00:00:12] Deleting ImageMagick7-7.0.11.12_3.pkg: no longer needed
[00:00:12] Deleting amavisd-new-2.12.0_1,1.pkg: no longer needed
[00:00:12] Deleting arc-5.21p.pkg: no longer needed
[00:00:12] Deleting arj-3.10.22_8.pkg: no longer needed
[00:00:12] Deleting atk-2.36.0.pkg: no longer needed
[00:00:12] Deleting awstats-7.8,1.pkg: no longer needed
[00:00:12] Deleting autoconf213-2.13.000227_7.pkg: no longer needed
[00:00:12] Deleting c-ares-1.17.2.pkg: no longer needed

Basically, "bulk -f" seems to have started preemptively deleting any
existing package that isn't specifically listed in the given file or
required by a port that is listed.  So much for building things in
stages!

This wasn't the case previously, and I can't find any flags that
control this behavior on the man page.

Is this intentional?  Is there a way to get it not to do that?  (Short
of modifying our build scripts not to use -f anymore.)

Thanks for any advice!