The Hystrix circuit doesn't close after the underlying service is back online

[maxithub]

I followed this https://github.com/livelessons-spring/building-microservices/tree/master/livelessons-choreography/livelessons-choreography-hystrix, everything works just fine. The circuit was opened after some seconds I stopped the contact-service. But when I started it again, it wasn't closed automatically. The circuit seems remain open forever.