To reproduce it first run the DDL statements:

create table cs1(i bigint) engine=columnstore;
alter table cs1 add column v1 varchar(1);

After that one must insert > 8kk rows into the table. I have simple generator for the purpose so feel free to ask for it.
After the preparations call
SELECT * FROM cs1 LIMIT 0, 1000;
and check logs.

There is a shortcut. Instead of populating the table with values just run:
select c.object_id,c.column_name,e.width from information_schema.columnstore_extents e, information_schema.columnstore_columns c where e.object_id = c.object_id and c.column_name = 'v1';

The width returned for the column must be 4 instead of 2 that is the correct value.

Please review.

The fix doesn't appear to work in all cases, more information in the PR

Also can you please provide a test case in the regression suite?

Please review the change.

Build verified: 1.1.7-1 nightly

MariaDB [mytest]> alter table cs1 add column v1 varchar(1);
Query OK, 0 rows affected (0.12 sec)
Records: 0 Duplicates: 0 Warnings: 0

MariaDB [mytest]> select c.object_id,c.column_name,e.width from information_schema.columnstore_extents e, information_schema.columnstore_columns c where e.object_id = c.object_id and c.column_name = 'v1';
---------------------------

---------------------------

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1 row in set (0.37 sec)