Parallel pipeline with 2 inline stages

Playing with Jenkins pipeline from https://www.jenkins.io/doc/pipeline/examples/#parallel-multiple-nodes

Simple two parallel steps (OK)

I made a first test pipeline this way:

pipeline {
   stages {
      stage('Build') {
         steps {
            script {
                def labels = ['precise', 'trusty'] // labels for Jenkins node types we will build on
                def builders = [:]
                for (x in labels) {
                    def label = x // Need to bind the label variable before the closure - can't do 'for (label in labels)'
                
                    // Create a map to pass in to the 'parallel' step so we can fire all the builds at once
                    builders[label] = {
                        node('JenkinsNode') {
                           sh script: 'echo build', label: 'Build on $env.NODE_NAME'
                        }
                    }
                }
                parallel builders
            }
         }
      }
   }
}

It resulted in the following expected diagram in Blue Ocean view:

Simple two parallel steps with two sub steps each (KO)

Attempt#1

Then I tried to split each parallel step in two inline stages (to simulate build and tests for example)

pipeline {
   stages {
      stage('Build') {
         steps {
            script {
                def labels = ['precise', 'trusty'] // labels for Jenkins node types we will build on
                def builders = [:]
                for (x in labels) {
                    def label = x // Need to bind the label variable before the closure - can't do 'for (label in labels)'
                
                    // Create a map to pass in to the 'parallel' step so we can fire all the builds at once
                    builders[label] = {
                        node('JenkinsNode') {
                            stage("build") {
                                sh script: 'echo build', label: 'Build on $env.NODE_NAME'
                            }
                            stage("test") {
                                sh script: 'echo run unit tests', label: 'Run unit tests on $env.NODE_NAME'
                            }
                        }
                    }
                }
                parallel builders
            }
         }
      }
   }
}

The Jenkins logs show both build and test stages are run for each parallel step, but the Blue Ocean view only states build stage:

I would expect something like:

I'm not very clear about the boundaries between declarative and scripted pipelines, but I suspect a misunderstanding around this.

Attempt#2

Following a suggestion in comments, I slightly changed the code to have sub-stages unique names (build1, test1, build2, test2) and it does not change the diagram. I still have build steps only.

Here are the Jenkins logs in this case:

Question: Is the pipeline invalid (leading to only "build" sub-steps instead of build + test sub-steps) or is it a limitation of Blue Ocean (1.25.3)?