Wrong column default values

Hi,

I have installed Postgres 8.3.8 on Fedora Linux and I access it per
JDBC (PostgreSQL 8.1 JDBC3 with SSL (build 407)). If I create a table,
the default values will be set by the database to

NULL::timestamp without time zone

for a timezone column and to

NULL::character varying

for a varchar column. How I can prevent such a behaviour? Both column
defaults should be NULL. Any ideas?

Thanks
Andre