BUG #1651: static date field is not recognized automatically when group by is used

The following bug has been logged online:

Bug reference:      1651
Logged by:          Peter van der Meer
Email address:      peter.vd.meer@yifan.net
PostgreSQL version: 7.4.7-6
Operating system:   Debian Linux (Unstable)
Description:        static date field is not recognized automatically when
group by is used
Details:

This is the table I used for testing:
 CREATE TABLE testthis(id INT PRIMARY KEY, somedate DATE);

This query works as expected:
  INSERT INTO testthis(id, somedate) SELECT 1 as id, '2005-02-02' as
somedate;

This query doesn't work:
  INSERT INTO testthis(id, somedate) SELECT 2 as id, '2005-02-02' as
somedate GROUP BY id, somedate;
Executing it reports:
 ERROR:  column "somedate" is of type date but expression is of type text

A possible workaround is explicit typecasting:
  INSERT INTO testthis(id, somedate) SELECT 2 as id, '2005-02-02'::Date as
somedate GROUP BY id, somedate;
(This works as expected again.)

The example SELECT in the INSERT INTO query here doesn't need GROUP BY, but
I'm sure one could think of a SELECT in a INSERT INTO query where a date is
given static and GROUP BY is neccecary for calculating an aggregrate-result.