Problem with fixed length fields.

Platform:
Postgres 7.4.5, lastest JDBC driver from CVS.

Table:
create table t(a char(2),b char(2));
insert into t values ('  ','  ');

Jdbc:

This query finds nothing
PreparedStatement st = db.prepareStatement("select * from t where a=?
and b=?");
st.setString(1,"  ");
st.setString(2,"  ");
ResultSet rs = st.executeQuery();

This query works
rs = db.prepareStatement("select * from t where a='  ' and b='
'").executeQuery();

Why?