Booktitle of new type fields

[Jarmill]

I would like to create a category called @unpubproceedings with type_names: {unpubproceedings: Conference Articles (accepted)}.

When I perform this, the booktitle field in the bibtex file is ignored. All work of type @unpubproceedings inherit the booktitle of the most recent @INPROCEEDINGS.

Is there a way to explicitly set the booktitle fields of this new type?

-jarmill