Domain inclusion seem to not work

I've got the following in my project.conf:

split-rules:
  devel:
  # Those are the default BuildStream ones
  - |
    %{includedir}
  - |
    %{includedir}/**
  - |
    %{libdir}/lib*.a
  - |
    %{libdir}/lib*.la
  - |
    %{libdir}/pkgconfig/*.pc
  - |
    %{datadir}/pkgconfig/*.pc
  - |
    %{datadir}/aclocal/*.m4
  # Those are the ones I added
  - |
    %{bindir}/*gcc*
  - |
    %{libexecdir}/gcc

I have a compose element with:

config:
  include:
  - runtime
  - locale

I would expect that element not to have any of the things I added to the devel domain. And yet, when I bst checkout it, there they are.

Am I doing something wrong? Or did I stumble upon a bug?

(edited to explicitly mention I was using a compose element)