This was noticed by jglick in the latest pipeline aggregator demo, during the dev phase, when running it (only during the execution of that phase though):

When you run the stage, which boils down to the below, the first time it runs you see duplicate shell steps showing as runtime of 47+ years, which turns into the correct value after a few seconds:

stage('Dev') {
    node {
        git 'git://localhost/repo'
        mvn '-o clean package'
        dir('target') {stash name: 'war', includes: 'x.war'}
    }
}
def mvn(args) {
    sh "sleep 10 && ${tool 'Maven 3.x'}/bin/mvn ${args}"
}

I can reproduce duplicate steps like this:

stage('sample') {
    node {
        echo 'do stuff'
        sh 'sleep 15'
        dir('sample') {
            sh 'sleep 5'
        }
    }
}