Interesting – I first did a print preview and the “add a new column” did not appear in the report. Then I hide the column and got the same results. However, when I tried in insert a column into the table, nothing happened and the column would not insert. I then closed the file without saving changes and it would still not allow me to insert a column. A new file would let me insert a column.
I think you might have found a bug – I will run it up the ladder and see what they can do. I am running 2010 Pro SP1.
FYI – there is not a column called “add a new column”. To follow up my direct email is email@example.com