Wrong result with aggregate function as a window function

create table t4 (i int);

insert into t4 values (1),(2);

select i, sum(i) over (partition by i) from t4;

+------+------------------------------+

| i    | sum(i) over (partition by i) |

+------+------------------------------+

|    1 |                            3 |

|    2 |                            2 |

+------+------------------------------+

2 rows in set (0.00 sec)

postgres=# select i, sum(i) over (partition by i) from t4;

 i | sum 

---+-----

 1 |   1

 2 |   2

(2 rows)

MariaDB [test]> select i, sum(i) over (partition by i order by i) from t4;

+------+-----------------------------------------+

| i    | sum(i) over (partition by i order by i) |

+------+-----------------------------------------+

|    1 |                                       1 |

|    2 |                                       2 |

+------+-----------------------------------------+

2 rows in set (0.00 sec)