Java: platform plugin does not align dependencies on all projects

I watched the ‘Dependency Management with Gradle Part 2’ webinar, and found that the plaform plugin was what I had been expecting to align dependencies, so I tried to use but I don’t get quite the result I hoped for.
I took the example project “dependencyAlignmentWithPlatform” and made the following modifications:

  • added a dependency to waffle-jna in the lib subproject (transitive dependency towards Guava 19)
  • added a dependency to google-cloud-vision in the utils subproject (transitive dependency towards Guava 26.0)

I would have expected that the Guava version would be 26.0 everywhere, but the lib subproject still uses version 19.
I have put the project on github : dependencyAlignmentWithPlatform
Is there something I misconfigured or have I misunderstood what the plaform plugin can do in terms of dependency alignment in projects?