Fails to rename column when alter renames + re-adds new column with prev name

[casassg]

When renaming a column and then re-creating it within the same ALTER statement, gh-ost deletes the entiretity of the name-changed column.

Example:

-- regular alter table (expected behaviour)
CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, c1 VARCHAR(100), c2 VARCHAR(100));
INSERT INTO t1 (c1, c2) VALUES ('a', 'b'), ('c', 'd'), ('e', 'f');
ALTER TABLE t1 RENAME COLUMN c1 TO n1, ADD COLUMN c1 varchar(100);
SELECT * FROM t1;
+----+------+------+------+
| id | n1   | c2   | c1   |
+----+------+------+------+
|  1 | a    | b    | NULL |
|  2 | c    | d    | NULL |
|  3 | e    | f    | NULL |
+----+------+------+------+

Using gh-ost:

go run . \
--max-load=Threads_running=25 \
--critical-load=Threads_running=1000 \
--chunk-size=1000 \
--user="[REDACTED]" \
--password="[REDACTED]" \
--host="127.0.0.1" \
--port=8030 \
--allow-on-master \
--database="test" \
--table="t1" \
--verbose \
--initially-drop-old-table \
--ok-to-drop-table \
--execute  --initially-drop-ghost-table --alter="RENAME COLUMN c1 TO n1, ADD COLUMN c1 varchar(100)"

Result:

+----+------+------+------+
| id | n1   | c2   | c1   |
+----+------+------+------+
|  1 | NULL | b    | a    |
|  2 | NULL | d    | c    |
|  3 | NULL | f    | e    |
+----+------+------+------+