Repeated calls to scatter with identical data produce different axis limits #15955

Bug report

Bug summary

In trying to debug some tests, I discovered some strange behavior. I'm not certain it's a bug, but I can't really think of an explanation for it, so I'm reporting.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt

f, ax = plt.subplots()
x, y = np.random.randn(2, 50)
ax.scatter(x, y)
xlim = ax.get_xlim()
ax.scatter(x, y)
print(xlim == ax.get_xlim())

Actual outcome

False

Expected outcome

True

Other observations

It appears to be scatter dependent. If I replace both calls to scatter with plot, it passes. Calling scatter then plot passes, but calling plot then scatter fails.

Matplotlib version

• Operating system: MacOS
• Matplotlib version: '3.1.1'
• Matplotlib backend (print(matplotlib.get_backend())): notebook inline, reproduces on Agg
• Python version: 3.7