为何Spark Cassandra Connector的LocalNodeFirstLoadBalancingPolicy会添加非本地DC节点？

根据LocalNodeFirstLoadBalancingPolicy的官方文档说明：

优先选择本地节点，之后以随机顺序选择本地数据中心（DC）的节点，绝不会选择其他数据中心的节点。对于写入操作，如果语句设置了路由键，该负载均衡策略（LBP）具备令牌感知能力——相比其他节点，会优先选择计算出的令牌对应的副本节点。

但在实际Spark作业运行日志中，观察到集群内所有节点都被程序识别纳入，具体日志片段：

21/05/05 10:08:40 INFO CassandraWriter$: Setting local_dc: DC1
21/05/05 10:08:40 INFO CassandraWriter$: Writing to DC: DC1, available host ips: x.x.x.54,x.x.x.237,x.x.x.168,x.x.x.197,x.x.x.219
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.219:9042 added
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.237:9042 added
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.54:9042 added
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.238:9042 added
21/05/05 10:08:41 INFO LocalNodeFirstLoadBalancingPolicy: Added host x.x.x.238 (DC2)
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.168:9042 added
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.42:9042 added
21/05/05 10:08:41 INFO LocalNodeFirstLoadBalancingPolicy: Added host x.x.x.42 (DC2)
21/05/05 10:08:41 INFO Cluster: New Cassandra host /x.x.x.109:9042 added
21/05/05 10:08:41 INFO LocalNodeFirstLoadBalancingPolicy: Added host x.x.x.109 (DC2)

核心疑问：为什么DC2的节点会被策略添加？按照对策略的理解，协调节点应当始终从配置的local_dc范围内选取。
测试过程中尝试过不设置spark.cassandra.connection.local_dc参数运行数据摄入任务，也观测到了完全一致的日志表现。
对应的写入实现代码如下：

records.write.cassandraFormat(table, keySpace)
  .mode(SaveMode.Append)
  .option(CassandraConnectorConf.LocalDCParam.name, cassandraDC.name)
  .option(CassandraConnectorConf.ConnectionHostParam.name, cassandraDC.availableHosts.mkString(","))
  .save()

补充场景说明：Spark集群与Cassandra集群部署相互独立，当前使用场景为从Spark集群向Cassandra集群批量写入数据。

内容的提问来源于stack exchange，提问作者Ana