Casting timestamp

Hi all, 
I posting this again...
Why the second casting don't work?

--- start with this 
set datestyle = 'iso'; 
show datestyle; 
select current_timestamp::text::timestamp; 
--- now try this 
set datestyle = 'postgres'; 
show datestyle; 
select current_timestamp::text::timestamp; 
   In the first one, I get          timestamptz 
------------------------------- 2002-05-13 10:19:55.158434-03 
   In the last one, I get 
ERROR:  Bad timestamp external representation 'Mon May 13 10:19:56.671847 
2002 BRT' 


   []'s
   Edipo Elder F. de Melo