Why cannot kakfka copy data to a new replica automatically when one of replica is down?

[wuchang]

I have a kafka clusters with 3 brokers. 192.168.80.82,192.168.80.146 and 
192.168.80.110
This is the topic description named DruidAppColdStartMsg:

[appuser@hz-192-168-80-146 kafka]$ bin/kafka-topics.sh --describe --topic 
DruidAppColdStartMsg --zookeeper 10.120.241.50:2181
Topic:DruidAppColdStartMsg      PartitionCount:2        ReplicationFactor:2     
Configs:
        Topic: DruidAppColdStartMsg     Partition: 0    Leader: 82      
Replicas: 82,146        Isr: 82,146
        Topic: DruidAppColdStartMsg     Partition: 1    Leader: 110     
Replicas: 110,82        Isr: 110,82

Obviously , the replication-factor of this topic is 2 , everything is ok.
Then , my 192.168.80.146 broker  is down for some reason.

[appuser@hz-192-168-80-146 kafka]$ bin/kafka-topics.sh --describe --topic 
DruidAppColdStartMsg --zookeeper 10.120.241.50:2181
Topic:DruidAppColdStartMsg      PartitionCount:2        ReplicationFactor:2     
Configs:
        Topic: DruidAppColdStartMsg     Partition: 0    Leader: 82      
Replicas: 82,146        Isr: 82
        Topic: DruidAppColdStartMsg     Partition: 1    Leader: 110     
Replicas: 110,82        Isr: 110,82
From the Isr, the 146 is missing.I cannot  produce  message by 
kafka-console-producer to this topic  unless I restart the 192.168.80.146 
broker.

My question is , why kaka doesn’t make the active broker 192.168.80.110 to 
replace 192.168.80.146 as a new Isr for DruidAppColdStartMsg-0  ?
Is any configuration missing?
Thank you very much.