strange problem with plpgsql

I have a strange problem with a plpgsql function. Here is the code :

      create function tg_survey_au() returns opaque as '
      begin
        if new.dateexpire != old.dateexpire or new.email != old.email then
           insert into survey_log values (
              current_timestamp,
              ''update'',
              new.idxsurvey,
              new.dateexpire,
              new.email
           );
         end if;
       return new;
      end;
      ' language 'plpgsql';

      create trigger tg_survey_au after update on survey for each row execute procedure tg_survey_au();
 

The problem is about the 'or' in the if statement. I have tested the if statement with just one condition. One with dateexpire and one with email. It works very well. Then I have joined the two conditions in the if statement with an 'or' like here in the code. Then, I have an insert in survey_log just when the email change, not if the dateexpire change! It seems that the 'or' does not work.

Any idea ?

Note : The tests have been tested on a postgresql version 7.0.2 on a RedHat Linux 6.2 machine.

--
Richard NAGY
Presenceweb / Nameshield