Bug #65731 ALTER IGNORE behaves differently than documented

Description:
The documentation states: "If IGNORE is specified, only the first row is used of rows with duplicates on a unique key. The other conflicting rows are deleted. Incorrect values are truncated to the closest matching acceptable value."

However, that is clearly not the actualy behavior:

mysql> create table ignore_test (
    ->   c1 int not null,
    ->   c2 int not null)
    -> engine=innodb;
Query OK, 0 rows affected (0.01 sec)

mysql> insert into ignore_test values (1,1), (1,2), (2,1), (2,2);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> alter ignore table ignore_test add primary key (c1,c2), add index (c1), add index (c2);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from ignore_test;
+----+----+
| c1 | c2 |
+----+----+
|  1 |  1 |
|  1 |  2 |
|  2 |  1 |
|  2 |  2 |
+----+----+
4 rows in set (0.00 sec)

mysql> show create table ignore_test\G
*************************** 1. row ***************************
       Table: ignore_test
Create Table: CREATE TABLE `ignore_test` (
  `c1` int(11) NOT NULL,
  `c2` int(11) NOT NULL,
  PRIMARY KEY (`c1`,`c2`),
  KEY `c1` (`c1`),
  KEY `c2` (`c2`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

How to repeat:
See main description.

I do not see any problem. You added primary (and thus unique) key like this:

primary key (c1,c2)

and all your rows are unique by these 2 columns, (1,1), (1,2), (2,1) and (2,2). Other indexes are non-unique by default. So, why do you expect any other output?

haha yes you're right, I copied incorrectly.  What it *should* have said was:

mysql> create table ignore_test (   c1 int not null,   c2 int not null) engine=innodb;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into ignore_test values (1,1), (1,2), (2,1), (2,2);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> insert into ignore_test values (1,1), (1,2), (2,1), (2,2);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> alter ignore table ignore_test add primary key (c1,c2), add index (c1), add index (c2);
ERROR 1062 (23000): Duplicate entry '1-1' for key 'PRIMARY'
mysql> 

If I understand the manual correctly, this should have succeeded and the duplicate data been deleted?

Thank you for the feedback.

This is duplicate of bug #40344.