Trouble combining rust versions with os in matrix

I am trying to run tests on linux, win and mac. I would like that to test both stable and nightly on each of those. The trouble starts when I take this configuration and modify the rust: nightly entry at the top to include both nightly and stable.

I was expecting it to run the matrix and run each of those on both versions of rustc, but instead I get:

  • linux: nightly + 2 times stable
  • windows and mac: just stable.

Is there a way to make this work without having to duplicate all the instructions in each matrix variant for both rustc versions?