CIS Spreadsheet - Additional Unwanted Fields

I set up CIS using a spreadsheet with component families organized in separate tabs.

Within CIS some of the component families have a number of undefined fields added to the CIS listing: F9, F10, F11 etc.

Any ideas what is causing this?

I seem to recall a document describing specifics of the spreadsheet requirements but can't locate this. Thought it contained something about defining data ranges as "table" etc. - does anyone know if such a document exists?