ipywidgets in frozen cell are duplicated every time notebook is reloaded.

[shingo78]

1. Make the widget
   
2. Save the notebook and reload
   
3. Save the notebook and reload again
   

I assume that it is because CodeCell.clear_output function is not working in frozen cell by #7.
Notebook.render_cell_output function calls clear_output function.
https://github.com/jupyter/notebook/blob/5.0.0/notebook/static/notebook/js/notebook.js#L1685
ipywidgets calls Notebook.render_cell_output function for rendering widget.

[yacchin1205]

Also occurred on Notebook 5.7.0

[horietakehiro]

The exact same issue happens in the latest versions.

niicloudoperation/notebook:202201

jupyter core     : 4.7.1
jupyter-notebook : 6.3.0
qtconsole        : not installed
ipython          : 7.23.1
ipykernel        : 5.5.4
jupyter client   : 6.1.12
jupyter lab      : 3.0.14
nbconvert        : 6.0.7
ipywidgets       : 7.6.3
nbformat         : 5.1.3
traitlets        : 5.0.5