Bug report

Bug summary

Minor ticklabels are missing at positions of major ticks.

Code for reproduction

import numpy as np
import matplotlib.dates as mdates
import matplotlib.pyplot as plt

t = np.arange("2018-11-03", "2018-11-06", dtype="datetime64")
x = np.random.rand(len(t))

fig, ax = plt.subplots()
ax.plot(t,x)

ax.xaxis.set_major_locator(mdates.DayLocator())
ax.xaxis.set_major_formatter(mdates.DateFormatter('\n%a'))

ax.xaxis.set_minor_locator(mdates.HourLocator((0,6,12,18)))
ax.xaxis.set_minor_formatter(mdates.DateFormatter('%H:%M'))

plt.show()

Actual outcome

The above code run with current master produces

The minor ticklabels showing the 00:00 hours are missing.

Expected outcome

The expected outcome would be the same as when running the code with matplotlib 3.0.2 or below:

I would expect to see the hours throughout.

Matplotlib version

• Operating system: Win8
• Matplotlib version: master
• Matplotlib backend (print(matplotlib.get_backend())): any
• Python version: 3.6