Bug 7993 has introduced a problem with the display of saved reports. If a saved report has a type it will appear twice in the list. There are not duplicates in the database, just in the list.
Sorry, it's not the type that causes the problem for me, it's the report_group. Reports which have report_group set appear twice under the "all" tab.
It's a data problem on my end. All my "report_group" authorised_values were duplicated in my database.