These should be equal, but they are not on master:

import numpy as np
import matplotlib.pyplot as plt

fig_test = plt.figure()
fig_ref = plt.figure()

x = np.arange(4)
y = np.arange(7)
X, Y = np.meshgrid(x, y)
C = X + Y

ax = fig_test.subplots()
ax.pcolormesh(C, shading="nearest")

ax = fig_ref.subplots()
ax.pcolormesh(x, y, C, shading="nearest")

plt.show()

On main the first figure is

and the second figure is

With this change they are both the same, and look like the second figure.

Closes #29179

PR summary

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines