extend differences

Can anyone tell me why the extend function behaves differently for attributes and for constants? Here is an example: create table D (d date); create table DT (dt datetime year to fraction(2)); insert into D values ('10/28/1988'); insert into DT values ('1988-10-28 06:01:00.00'); -- returns no data, as you would expect it not to: the date is promoted to a datetime, same date but at midnight select * from Da, DTa where d = dt; -- this statment does return data. It appears as if the datetime is truncated to a date... select * from Da, DTa where Da.d = extend('1988-10-28 06:01:00.00', year tofraction(5)); -- this statment returns exactly the same string as in the literal in the previous statement select extend('1988-10-28 06:01:00.00', year to fraction(5)) as x from DT Explicitly converting the datetime string to a datetime then extending the qualifier does not work, either. Am I missing something? Ben