Shiftdata breaks pcolormesh wrapping

[matt-kendall]

I have a data grid which spans the whole globe from -180 -> 180. pcolormesh can plot this OK if I have lon_0=0 in which case Basemap doesn't have to do any wrapping

However if I do this for lon_0=180 (where Basemap has to shift some data), I get the following incorrect plot:

The code I have used for this is (using 1.0.7):

    import numpy as np
    from mpl_toolkits.basemap import Basemap
    import matplotlib.pyplot as plt
    x = np.arange(-180, 190, 10)
    y = np.array([40, 50, 60])
    data = np.arange(72).reshape((2, 36))
    xv, yv = np.meshgrid(x, y)
    # Add an empty row and column of data so that the data is the same shape as X,Y
    wider_data = np.ma.zeros(xv.shape)
    for index, v in np.ndenumerate(data):
        wider_data[index] = data[index]
    for lon in (0, 180):
        map = Basemap(lon_0=lon)
        map.drawparallels(np.arange(-90, 90, 20), labels=[1, 1, 0, 1])
        map.drawmeridians(np.arange(-180, 180, 30), labels=[1, 1, 0, 1])
        map.pcolormesh(xv, yv, wider_data, latlon=True)
        map.drawcoastlines()
        plt.show()

I suspect that this problem is related to #182 because to get around that issue, I have had to add an empty row and column to the data. This should still be OK though, since that extra data should just be ignored (from the pcolormesh docs).

However, what actually happens is that the empty row gets moved around because shiftdata doesn't know it should ignore and so the plot is wrong.