SQL & PL/SQL

I am using version 11.2.
I am trying to execute a select statement on a table from remote site. My dirving_site hint is getting ignored. I was wondering if any body has any theories about this.

My remote table is remote_tab( col1 varchar2(11), col2 varchar2(6));

-- driving_site hint is not ignored
select /*+ driving_site(rt) */ col1, max(col2) from remote_tab@dblink rt group by col1;

-- driving_site hint ignored
select /*+ driving_site(rt) */ col1, max(to_date(col2, 'RRMMDD')) from remote_tab@dblink rt group by col1;

Any idea on why to_date function causes driving_site hint to be ignored?