NPEs on node restart

Setup:
3 nodes with torus,10,10 topo (each switch is connected to all controller nodes)
In a running system, restart onos2. The following errors are observed in onos2 logs during its start up:

2016-01-05 00:49:33,172 | ERROR | message-handlers | Tools | 73 - org.onosproject.onlab-misc - 1.5.0.SNAPSHOT | Uncaught exception on onos-store-flow-message-handlers
java.lang.NullPointerException
at org.onosproject.net.flow.impl.FlowRuleManager$InternalStoreDelegate.notify(FlowRuleManager.java:511)[118:org.onosproject.onos-core-net:1.5.0.SNAPSHOT]
at org.onosproject.net.flow.impl.FlowRuleManager$InternalStoreDelegate.notify(FlowRuleManager.java:458)[118:org.onosproject.onos-core-net:1.5.0.SNAPSHOT]
at org.onosproject.store.AbstractStore.notifyDelegate(AbstractStore.java:58)[75:org.onosproject.onos-api:1.5.0.SNAPSHOT]
at org.onosproject.store.flow.impl.NewDistributedFlowRuleStore$$Lambda$346/1608645988.accept(Unknown Source)[120:org.onosproject.onos-core-dist:1.5.0.SNAPSHOT]
at org.onosproject.store.cluster.messaging.impl.ClusterCommunicationManager$InternalMessageConsumer.accept(ClusterCommunicationManager.java:258)[120:org.onosproject.onos-core-dist:1.5.0.SNAPSHOT]
at org.onosproject.store.cluster.messaging.impl.ClusterCommunicationManager$InternalMessageConsumer.accept(ClusterCommunicationManager.java:247)[120:org.onosproject.onos-core-dist:1.5.0.SNAPSHOT]
at org.onlab.netty.NettyMessaging.lambda$null$1(NettyMessaging.java:208)[123:org.onosproject.onlab-netty:1.5.0.SNAPSHOT]
at org.onlab.netty.NettyMessaging$$Lambda$20/1024549477.run(Unknown Source)[123:org.onosproject.onlab-netty:1.5.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_31]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_31]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_31]

These errors don't seem to impact the operation state of the system.