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?