Actually it's an unfinished part of #9227. We already don't add CAST in alters, after this, we will not add them in create/attach queries.

It's a bug fix because if the user added column with default with ALTER query to the replicated table and executed detach/attach clickhouse will not be able to attach table. Metadata in ZK for the new column stored without CAST both in zookeeper and .sql file, but InterpreterCreateQuery will add cast in memory (before table startup) and after that will try to compare this in-memory struct with data in zookeeper. The check will fail.

If old version created a table with CAST expressions in defaults we will read them from .sql and from the zookeeper. For new tables, we will store defaults without casts also in both places. It should work well.

If old version created a table with CAST expressions in defaults we will read them from .sql and from the zookeeper. For new tables, we will store defaults without casts also in both places. It should work well.

in case if the table was created on the old version with the CAST, and adding a replica with a new version will complain:
Table columns structure in ZooKeeper is different from local table structure