Problem using Ortho projection and shadedrelief on a sector of the globe

[baccandr]

I'm trying to plot a sector of the world in basemap using an orthographic projection and I would like to have a shadedrelief background.

If I don't use shadedrelief everything works fine:

import numpy as np
from mpl_toolkits.basemap import Basemap
import matplotlib.pyplot as plt
   
fig = plt.figure()
ax = fig.add_subplot(111)
   
m = Basemap(projection='ortho',lon_0 = 0, lat_0 = 40,
           llcrnrx=-3000000, llcrnry=1000000, urcrnrx=3000000, urcrnry=7000000, 
           resolution = 'l')
   
m.drawcoastlines()
m.fillcontinents(color='coral',lake_color='aqua')
   
# draw parallels and meridians.
m.drawparallels(np.arange(-90.,120.,30.))
m.drawmeridians(np.arange(0.,420.,60.))
m.drawmapboundary(fill_color='aqua')

However, when I add the command m.shadedrelief() (after removing the m.drawmapboundary and the m.fillcontinents commands) I get the following graph:

Apparently the problem is that the background is not restricted to the bounding box I set in the basemap command. I tried also with other backgrounds (e.g. bluemarble) but I get the same problem.

p.s. This is a copy of a thread that I opened on stackexchange, sorry for the cross-posting!