BUG #4372: TO_DATE with ISO week and day

The following bug has been logged online:

Bug reference: 4372
Logged by: Kees Westerlaken
Email address: kees(dot)westerlaken(at)valuecare(dot)nl
PostgreSQL version: 8.3.3
Operating system: Windows
Description: TO_DATE with ISO week and day
Details:

The TO_DATE conversion with ISO week (IW) and ISO day (ID) format accepts
invalid values and sometimes returns wrong result.

select to_date('2008-31-4','IYYY-IW-ID')
results in "2008-07-31", which is correct

The valid values for IW are 1-7, however:
select to_date('2008-31-8','IYYY-IW-ID')
results in "2008-08-04" of which you could argue if it is correct.

However:
select to_date('2008-31-10','IYYY-IW-ID')
results in "2008-07-28", which is not correct

And even worse: if you use the IW and ID format in an older version it
works, but the result is wrong.
select to_date('2008-31-4','IYYY-IW-ID')
in version 8.2.6 results in "2004-07-26", which is wrong.