Bug report

Bug summary
If there are multiple curves with the same label in a figure/subplot, only the last one of them can be selected in the Figure options window under the Curves tab. In the legend however, they appear as they should.

Code for reproduction

import matplotlib.pyplot as plt
plt.plot([0,1],[0,1],label="line")
plt.plot([0,1],[1,0],label="line")
plt.legend()
plt.show()

Actual outcome
See description above and the image below.

Expected outcome
All curves should be listed in the Figure options window, even if they have the same label.

Matplotlib version

• Operating system: Windows 10
• Matplotlib version (import matplotlib; print(matplotlib.__version__)): 3.3.4
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: 3.8.5
• Jupyter version (if applicable): -
• Other libraries: -

Matplotlib has been installed with pip.