Cannot hide field with exclude from display

I'd like to add a content taxonomy field to a content type, provide a default value for the field, and hide it from the user. Thus, every node of that content type is tagged with the appropriate taxonomy terms without the user having to enter them. I use the terms associated with this content type to create the url for the node.

Everything works, except checking 'Exclude' under 'Display Fields' for the content type does not hide the field from the user. Is there a way to make this work?

I'm using Drupal version 6.22 and Content Taxonomy 6.x-1.0-rc2.

Thanks for any help.