The kafka and elasticsearch output plugins won't block each other in one pipeline

When I upgrade logstash from version2.3.3 to 2.4.0, I find out the logstash outputs won't block each other.
In my enviroment, the output plugins are kafka 0.10 and elasticsearch 2.3.4.
When kafka is down , the elasticsearch can still have event input.

Is this right?

{:timestamp=>"2016-09-02T08:37:46.891000+0800", :message=>"Beats input: the pipeline is blocked, temporary refusing new connection.", :reconnect_backoff_sleep=>0.5, :level=>:warn}

this warn was never shown again

Does anyone have the same problem?
Can someone help?