recalculate request parameters in scheduled requestset

Hi,

We have a requestset scheduled for every night. For some programs it's required to have a date_to parameter. We would like this date to be the end of the month. In order to achieve this I set the requestparameter in the set to:

Type: SQL-statement

Value: SELECT last_day(trunc(sysdate)) from dual

When I schedule the set, this works great...until we move to the next month: then the parameter is still the last day of the previous month. It seems that the parameters for the next run of the requestset are simply copied from the previous run of the set instead of being recalulated.