Bug report

Bug summary

When more than one figure is shown, then clicking on the last figure's close button or running plt.close() or plt.close('all') leaves a zombie figure behind. At first, figure windows are properly closed, but when switching back to the matplotlib python application, the last figure resuscitates and is not clickable nor closable anymore.

Doing the samething another time leaves an additional zombie figure window, and so on. The only way to close those non-responding windows is to quit ipython.

Code for reproduction

Running in ipython:

%matplotlib Qt5
import matplotlib.pyplot as plt
plt.figure()
plt.figure()
plt.close('all')

Actual outcome

No output, and the figures close. But then if we press alt-tab, the last figure resuscitates and does not respond to user input.

Expected outcome

The last figure should not resuscitate.

Matplotlib version

• Operating system: macOS 10.15.4
• Matplotlib version: 3.1.3
• Matplotlib backend (Qt5Agg):
• Python version: 3.7.7
• Other libraries:

Installation under conda, default conda channel:

conda create -n test python=3.7
conda activate test
conda install ipython matplotlib pyqt

[TAC edited to remove comments in example code to make copy-pasting easier]