Figures in Output disappear if Output displayed twice in same cell

使用提供的 Python notebook 示例重现该问题：在 Output widget 内创建 matplotlib 图形后调用 display(o) 两次。使用所列的 JupyterLab、ipympl、matplotlib 和 ipywidgets 版本比较第一次和第二次显示；当重复显示后图形仍然可见时，即表示完成。

Describe the issue

Got an odd one.
If an Output contains a figure, and one calls a single cell containing display(Output) twice, the output "empties" and no figure is shown.

Example below. One can emphasise it by first calling display(o) in one cell, and then doing the double call (I press ctrl + Enter twice) in another cell. I attach a figure showing the result.

# in one cell:
%matplotlib widget
import matplotlib.pyplot as plt
from ipywidgets import Output
o = Output()
with o:
    plt.figure()
    plt.plot([1,2,3])
# In a separate cell, call this twice after each other
display(o)

Versions

 3.8.2 | packaged by conda-forge | (default, Mar 23 2020, 17:32:17) [MSC v.1916 64 bit (AMD64)]
ipympl version: 0.5.6
jupyter core     : 4.6.3
jupyter-notebook : 6.0.3
qtconsole        : 4.7.2
ipython          : 7.13.0
ipykernel        : 5.2.0
jupyter client   : 6.1.3
jupyter lab      : 2.1.4
nbconvert        : 5.6.1
ipywidgets       : 7.5.1
nbformat         : 5.0.4
traitlets        : 4.3.3
Known nbextensions:
  config dir: C:\Users\thomasaar\.jupyter\nbconfig
    notebook section
      default_cells disabled
  config dir: C:\Users\thomasaar\.conda\envs\py5\etc\jupyter\nbconfig
    notebook section
      ipyvolume/extension enabled
      - Validating: ok
      jupyter-webrtc/extension enabled
      - Validating: ok
      jupyter-matplotlib/extension enabled
      - Validating: ok
      plotlywidget/extension enabled
      - Validating: ok
      jupyter-js-widgets/extension enabled
      - Validating: ok
    tree section
      ipyparallel/main enabled
      - Validating: ok
JupyterLab v2.1.4
Known labextensions:
   app dir: C:\Users\thomasaar\.conda\envs\py5\share\jupyter\lab
        @jupyter-widgets/jupyterlab-manager v2.0.0 enabled  ok
        @jupyter-widgets/jupyterlab-sidecar v0.5.0 enabled  ok
        jupyter-matplotlib v0.7.2 enabled  ok```