Problems with "pg.dropped" column after upgrade 9.5 to 9.6

Hi,

I've got very the similar problem as described in the message
with the subject "got some errors after upgrade poestgresql from 9.5 to 9.6".

I'll try to describe this very strange behaviour.

I have a table A which has some "pg.dropped" attribute in
pg_attribute table. It looks like:

select attname, attnum
from pg_attribute
where attrelid = A::regclass and attisdropped;

attname | attnum
-------------------------------+--------
........pg.dropped.57........ | 57
(1 row)

Now, I create SQL function doing only update on this table
when the boolean parameter of the function is True:

CREATE OR REPLACE FUNCTION _test_sql_update(in do_update boolean)
RETURNS VOID LANGUAGE sql VOLATILE AS $$
update A
set col = NULL
where do_update;
$$;

Now running:

select _test_sql_update(False);

returns this error:

ERROR: table row type and query-specified row type do not match
DETAIL: Query provides a value for a dropped column at ordinal position 57.
CONTEXT: SQL function "_test_sql_update" statement 1

If I don't use the parameter in "where" and instead I use the constant
False directly, everything works:

CREATE OR REPLACE FUNCTION _test_sql_update(in do_update boolean)
RETURNS VOID LANGUAGE sql VOLATILE AS $$
update A
set col = NULL
where False;
$$;

select _test_sql_update(False);

SQL=# _test_sql
-----------

(1 row)

If I define the function as plpgsql, everything is also working:

CREATE OR REPLACE FUNCTION _test_plpgsql_update(in do_update boolean)
RETURNS VOID LANGUAGE plpgsql VOLATILE AS $$
BEGIN
update A
set col = NULL
where do_update;
END;
$$;

My conclusion is:

The problem occurs only under these circumstances:

- Postgresql 9.6 (no problem in 9.5)

- SQL function doing update

- There is a boolean parameter of the fucntion used in the update command
and the table which is updated has some attisdropped attributes

Can anybody explain what is the problem?

Thanks
Pavel