wrong x-ticks for +/- 180°

[mathause]

I think the problem is that it is just at the edge of the plot.

import numpy as np
import mplotutils as mpu
import cartopy.feature as cfeature
import cartopy.crs as ccrs
import matplotlib.pyplot as plt

%matplotlib

f, ax = plt.subplots(1, 1, subplot_kw=dict(projection=ccrs.Robinson(central_longitude=180)))

#ax.coastlines()

ax.set_global()

lat = np.arange(-90, 91, 20)
lon = np.arange(-180, 181, 60)

mpu.xticklabels(lon, ax=ax, size=8)