6.5.3 - backend closes if wrong parameters to NULLIF, CASE

Continuing to try to work with the things.

I have a table "authors" with approx following fields:
( name text, id int4, birthdate date, ... , address_id int4 )

- when using a wrong CASE or NULLIF in INSERT/UPDATE 
statement on birthdate, it seems that it corrupts the 
address_id field.

Ie. If I do a thing like UPDATE authors set 
birthdate=NULLIF(date '12-12-1999', date '') ...

the backend will die and whenever afterwards I try to SELECT 
the address_id field from the updated row, it would die again.

If I do a SELECT NULLIF(date '12-12-1999', date '') it will 
correctly complain that '' is a wrong date value.

Seems also that when I try to UPDATE/INSERT using a CASE 
stmt it would die too, again corrupting the address_id field.