Why do batch updates to a CQL list merge the data?

I have created the following table CONSISTENCY LOCAL_QUORUM; drop keyspace if exists cycling; CREATE KEYSPACE IF NOT EXISTS cycling WITH REPLICATION = { 'class' : 'SimpleStrategy', 'replication_factor' : 3 } and durable_writes = true; CREATE TABLE IF NOT EXISTS cycling.rider ( rider_id int PRIMARY KEY, rider_name list, rider_name2 frozen> ); Do the following sequence of batch operations CONSISTENCY LOCAL_QUORUM; BEGIN BATCH UPDATE cycling.rider SET rider_name = ['a2'], rider_name2 = ['b2'] WHERE rider_id = 100; UPDATE cycling.rider SET rider_name = ['a3'], rider_name2 = ['b3'] WHERE rider_id = 100; APPLY BATCH; I get merged data in my list (rider_name) select * from cycling.rider; rider_id | rider_name | rider_name2 ----------+--------------+------------- 100 | ['a2', 'a3'] | ['b3'] Do you know why? I was expecting rider_id | rider_name | rider_name2 ----------+--------------+------------- 100 | ['a3'] | ['b3']