Duplicate Citation Being Thrown Despite Filter

[DKilkenny]

Describe the bug

I have a notebook repo which for simplicity sake has two notebooks and each notebook references the same citation. Despite using the filter described here at the bottom of each notebook, I am still getting a WARNING: duplicate citation for key "longuski2014optimal"

To Reproduce

1. Create a jupyter-book repo
2. Make two notebooks
3. Create a references.bib file and add the citation at the end of this list
4. Add {cite}`longuski2014optimal` to the notebook
5. Add the filter from the link above to the end of the notebook
6. Build the notebook

@book{longuski2014optimal,
  title={Optimal control with aerospace applications},
  author={Longuski, James M and Guzm{\'a}n, Jos{\'e} J and Prussing, John E},
  year={2014},
  publisher={Springer}
}

Expected behavior

No warnings.

Environment

• Python Version [e.g. 3.7.1]:
• Package versions or output of jupyter-book --version:

Jupyter Book      : 0.11.0a1
External ToC      : 0.1.0
MyST-Parser       : 0.13.6
MyST-NB           : 0.12.3
Sphinx Book Theme : 0.1.0
Jupyter-Cache     : 0.4.2
NbClient          : 0.5.2

• Operating System:

Additional context

Add any other context about the problem here.

[drsimonmartin]

I think the advice in the documentation is incorrect. The Sphinx docs recommend a different fix for this warning: "New in version 0.3.3. If you have multiple bibliographies, and you would like entries to be repeated in different documents, then use the keyprefix option."