As of 2.0b4, the order in which calls to set(xmargin=...) and set(xscale=...) are made result in different plots:

from matplotlib import pyplot as plt
fig, axs = plt.subplots(2)
axs[0].plot([1, 2], [1, 2])
axs[1].plot([1, 2], [1, 2])
axs[0].set(xscale="log"); axs[0].set(xmargin=0)
axs[1].set(xmargin=0); axs[1].set(xscale="log")
plt.show()

The ordering did not matter in 1.5, but that was because the setting of xmargin was effectively ignored :-)

I'm suggesting to milestone this to 2.0, but I'll let someone else make that call.