Note: This is not the same as https://issues.jenkins-ci.org/browse/JENKINS-46551 because a single step in the post { always { } } block succeeds even if the earlier steps {} block throws an exception.

The second "echo" statement in the post { always { } } section below fails with the exit code 127, which is the bash exit code from the earlier steps block attempt to run an arbitrary invalid shell command.

Whereas, including only a single step in the post { always { } } works as expected.

pipeline {
agent {
  docker {
    image 'python'
  }
}
  stages {
    stage('Run Tests') {
      steps {
        sh 'throwcommandnotfound'
      }
      post {
        always {
          echo 'this will succeed'
          echo 'this will fail'
        }
      }
    }
  }
}
 

 For the second screenshot below, I removed the second "echo" statement.