Content taxonomy: [Save to node] option pollutes Biblio Keyword list

G'Day Biblio folk,
We have a range of CCK fields to extend our biblio nodes, including some content taxonomy fields.
We want the field values to be saved onto the node as taxonomy field values, so we set the normal option to:
Save values additionally to the core taxonomy system (into the 'term_node' table).
However, this seems to have the effect of automatically adding these entries to the Biblio Keyword vocabulary as well...which means some fairly inappropriate terms get presented to users as if they were keywords from the publication.
Have I mis-set something along the way, or is this an obscure loose end?
Thanks as always,
JB