Inaccurate pipeline summary at startup

When running: bst build on the GNOME project, knowing that the base system is cached and need not be locally built, the pipeline summary is incorrect:

tristan@think:~/codethink/GNOME/gnome-modulesets$ bst build apps/meta-gnome-apps-tested.bst core/meta-gnome-core.bst
Loading:   245
Resolving: 245/245
Fetching artifact list from https://gnome7.codethink.co.uk/artifacts
Checking:  245/245

BuildStream Version 0.1.dev1510+g02539b8
  Session Start: Saturday, 11-11-2017 at 19:59:19
  Project:       gnome (/codethink/GNOME/gnome-modulesets)
  Targets:       apps/meta-gnome-apps-tested.bst, core/meta-gnome-core.bst

User Configuration
  Configuration File:      /home/tristan/.config/buildstream.conf
  Log Files:               /home/tristan/.cache/buildstream/logs
  Source Mirrors:          /home/tristan/.cache/buildstream/sources
  Build Area:              /home/tristan/.cache/buildstream/build
  Artifact Cache:          /home/tristan/.cache/buildstream/artifacts
  Maximum Fetch Tasks:     10
  Maximum Build Tasks:     4
  Maximum Push Tasks:      4
  Maximum Network Retries: 2

Project Options
  arch: x86_64

Pipeline
downloadable 76ebb4bb base/base-system.bst 
downloadable 9f432ec5 base/base-configure.bst 
      cached 3d363598 base/linker-priority.bst 
      cached e0372368 base/ninja.bst 
      cached f5c063a8 base/polkit-workaround.bst 
      cached f89419a4 base.bst 
     waiting 96cf2a1f core-deps/gettext.bst 
     waiting 61d4d541 core-deps/yelp-xsl.bst 
     ...
     ...

Here we are showing base/base-system.bst as downloadable, it is; except it's not going to be downloaded because it's a build-only dependency of base/base-configure.bst

The program works correctly and does not try to download the extra runtime artifact, but the pipeline summary somehow includes elements which are to be excluded form the session.