Imported a Library from where?
When you import, and the imported discovers
the source had custom (columns) metadata that do not currently exist in the current Library, it asks do you want to keep those (
not exact words).
You must have said Yes.
Even Standing on your head while re installing Calibre , will not get rid of them
Those columns ARE NOW in the current Library (structure). You will need to use the Add Columns feature to remove those. Note: There is no UNDO, so be careful
