When you Metadata->Export Keywords... from one catalog and then Metadata->Import Keywords... into another catalog the keywords in the new catalog that originally had all the export options unchecked now have the "Export Synonyms" and the "Export Containing Keywords" boxes checked in the new catalog. This means that potentially a lot of previously private information can be published without any warning.
The only way you can accurately replicate you Keyword List to a second catalog is to export the whole master catalog and delete all the images from the exported copy.