Bug ? different behaviour between 8.3 and 8.4 won IS NULL with sub arrays of nulls

Hi,

I found a difference of behaviour between 8.3 and 8.4 on IS NULL with 
multi-level arrays with NULL values.

I looked at the Changelog between 8.3 and 8.4, but I didn't find something 
really clear about this.

Is this a bug or a known issue or a normal, documented, 
difference of behaviour ?

See the following use case:

<~~~~~~~~~~~~~~~~~~~~~~~~
$ psql -p 5433 -U postgres -h localhost -c \
'SELECT substring(version() from 0 for 15),  ROW(NULL,NULL) IS NULL, ROW(ROW(NULL),NULL) IS NULL;'
   substring    | ?column? | ?column?
----------------+----------+---------- PostgreSQL 8.3 | t        | f
(1 ligne)

$ psql -p 5434 -U postgres -h localhost -c \
'SELECT substring(version() from 0 for 15),  ROW(NULL,NULL) IS NULL, ROW(ROW(NULL),NULL) IS NULL;'
   substring    | ?column? | ?column?
----------------+----------+---------- PostgreSQL 8.4 | t        | t
(1 ligne)
~~~~~~~~~~~~~~~~~~~~~~~~>

Regards,
-- 
Jehan-Guillaume (ioguix) de Rorthais
DBA
http://www.dalibo.com