xsite replication custom failurePolicy does not work with ASYNC strategy

I configure xsite backupFailurePolicy="CUSTOM" and specified failurePolicyClass (see below xml configuration).

When the strategy is set to "ASYNC", the failurePolicyClass code is never got invoked!!

But, same code will will be invoked if the strategy is set to "SYNC".

.....

<sites>
<backups>
<backup site="NYC" strategy="ASYNC" backupFailurePolicy="CUSTOM" failurePolicyClass="com.test.cluster.infinispan.CrossSiteReplicationFailurePolicy" timeout="12003"/>

</backups>
</sites>