Thanks for the patch. This fix already seems to be on the v1.1.x branch, but it didn't get correctly merged into master. Merging.

Good spot. Do you have a couple of lines of code to reproduce? I would be good to add a test for this.

This fix already seems to be on the v1.1.x branch.

The bug was introduced by me (in #706) and integrated into master. Hence, v1.1.x is free of this issue.

@ajdawson If you have the code to show the problem it would be still useful, but I may put the test in in another PR.

@pelson
I came across this while trying to write some tests for PR #766. I was planning on drawing several plots including colorbars with and without the extensions, which would show up this issue also.

I was thinking something along the lines of this (but a bit more comprehensive):

import numpy as np
import matplotlib.pyplot as plt


x = y = np.linspace(-np.pi, np.pi, 100)
X, Y = np.meshgrid(x, y)
Z = np.cos(Y) * np.sin(X)

levels_linear = [-.75, -.5, -.25, -0., .25, .5, .75]
fill = plt.contourf(x, y, Z, levels_linear, extend='max')
plt.colorbar(fill, orientation='horizontal')

The maximum extension is blue if the bug is present, and red otherwise.