Yes, this is a known bug:
From TODO list:
o ALTER TABLE ADD COLUMN column SERIAL doesn't create sequence
---------------------------------------------------------------------------
pgsql-bugs@postgresql.org wrote:
> wolfgang fuertbauer (w.fuertbauer@eunet.at) reports a bug with a severity of 3
> The lower the number the more severe it is.
>
> Short Description
> alter table add field serial - does not create serial field
>
> Long Description
> altering an existing table and adding a field from type serial via
>
> >>alter table test add (s serial);<<
>
> does not add a serial, but an integer field.
>
> Sample Code
> create table t (t text);
> CREATE
> \d t
> Table "t"
> Attribute | Type | Modifier
> -----------+------+----------
> t | text |
>
> alter table t add s serial;
> ALTER
>
> \d t
> Table "t"
> Attribute | Type | Modifier
> -----------+---------+----------
> t | text |
> s | integer |
>
>
> No file was uploaded with this report
>
>
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--
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