title: @Scheduled Expression with cron expression sometimes executes the task twice
body: <p>Scheduled task gets executed twice when using the cron expression with @Scheduled annotation.</p>
  
  <p>I am using @Scheduled(cron = "0 0 7-23 ? * 1-5") to execute a task on the hour from morning 7 till 23 pm. However, sometimes task gets executed twice</p>
  
  <pre><code>&gt;Running Task::LocalTime 2019-08-30T16:00:00
  &gt;Running Task::LocalTime 2019-08-30T17:00:00
  &gt;Running Task::LocalTime 2019-08-30T18:00:00
  &gt;Running Task::LocalTime 2019-08-30T18:59:58  (This shouldn't have executed)
  &gt;Running Task::LocalTime 2019-08-30T19:00:00
  &gt;Running Task::LocalTime 2019-08-30T19:59:59   (Neither should this)
  &gt;Running Task::LocalTime 2019-08-30T20:00:00
  &gt;Running Task::LocalTime 2019-08-30T21:00:00
  &gt;Running Task::LocalTime 2019-08-30T22:00:00
  </code></pre>
  
  <p>Am I doing something wrong ? When tried same expression with Spring/SpringBoot it seems to run correctly. </p>
  
  <p>Edit : Code</p>
  
  <pre class="lang-java prettyprint-override"><code>    package imbibing.oldman
          @Singleton
          public class NotifyHourlyToDrink {
              private static final Logger LOGGER = LoggerFactory.getLogger(NotifyHourlyToDrink.class);
              private int numberOfBeersDrank;
  
              @Scheduled(cron = "0 0 7-23 ? * 1-5")
              public void drinkBeer(){
                      numberOfBeersDrank++;
                      LOGGER.info("Oh! The chilled  number {}", numberOfBeersDrank);  
              }
          }
  
  </code></pre>