The report output for a scheduled report or a report for which you have not been prompted for values shows unexpected results. Another user may have modified the saved prompt values. If you have write access to a report and change the prompt values, those values are saved for everyone running the report after you.
To select different prompt values, you can run the report with options and select the check box next to Prompt for Values. If you consistently use prompts that differ from the majority of users, create a report view of the report in your personal folders.