Grid ylines and ticks are not drawn for y <= 0 in polar plots

Ex :

The bug is true in matplotlib 1.1.1 and 1.2.0. Thanks.

from matplotlib.pyplot import figure, show
import numpy as np

x = np.arange(0,7,0.001)
y = np.arange(-2.0,5.0, 0.001)
fig = figure()

ax = fig.add_subplot(111, polar=True)
ax.plot(x, y)
ax.autoscale_view(True,True,True)

fig.show()
raw_input()