string_to_array has to be stable?

Hello

I am working on to_array, to_string functions and I am looking on
string_to_array function. I am surprised so this function is marked as
immutable

postgres=# select array_to_string(array[current_date],',');array_to_string
-----------------2010-07-20
(1 row)

postgres=# set datestyle to German ;
SET
postgres=# select array_to_string(array[current_date],',');array_to_string
-----------------20.07.2010
(1 row)

it is probably wrong

Regards

Pavel Stehule