import matplotlib.pyplot as plt
import numpy as np

x = 1
y = 0

ux = 0
uy = 1


ax = plt.subplot()
ax.quiver(x, y, ux, uy, angles='xy')
plt.show()

I would expect this to plot a single arrow, with the tail at (0 ,1) and the head at (1, 1), but instead it seems to be shrunk and the head is at (1.01, 0):

Note the values of ux and uy can be changed to any positive numbers and exactly the same plot is generated.

This is on master, using the MacOSX backend.