When clicking (drilling down) into a summarized report of any type (column, bar, summary, summarized data table, pie, etc.). The columns shown cannot be edited. It appears to be a default set of columns that cannot be changed in any way.
The top level of a summarized report can be edited, the lower / sub levels cannot be edited.
The default columns are not very useful for most of our users, and the columns needed would differ based on the report. Not being able to modify this is quite a surprise as it is rather basic functionality.