Different Results in Reports & list

 while using  the same filter criteria for reports and 'Advanced Search lists' . We are getting different results. It should be same. The 'Advanced Search Lists' is showing correct results but reports are not showing all records.
Do you have any clue if there is some recent modifications happened in reporting module ? we rely a lot on reporting and if this is a flaw(which I am assuming)  then please confirm it to me. your help would be appreciable.

Thanks