error bars getting cut off when plotting

hi all,

i have the following simple plot using the 'errorbars' function. when
i plot it, one of the error bars is cut off:

from numpy import *
from scipy import *
from mpl_toolkits.axes_grid.axislines import SubplotZero
fig = plt.figure()
ax = SubplotZero(fig, 3, 2, 1)
for k in ["bottom", "top", "right"]:
m = array([0.8382035000000001, 0.81685835000000007])
sd = array([0.18543833, 0.12603507])
lw = 1.2
msize = 3
plt.errorbar([1, 2], m, yerr=sd, fmt='-s', markersize=msize, linewidth=lw)
tm = .8
lower_y = max(tm-.2, 0)
upper_y = min(tm+.4, 1)
ytickvals = arange(lower_y, upper_y + .1, .1)
plt.xlim([0, 3])
plt.ylim([lower_y, upper_y])

when i plot it, the top error bar of the first data point gets cut
off. this error bar should be at location:
0.8382035000000001+0.18543833 which slightly exceeds the ylimit of 1.
since the y value here is a probability, i dont want the plot to have
labels on it that exceed 1, since that does not make sense. is there
any way to allow more room for the y axis without plotting values
greater than 1? this is only for the purpose of errorbars. again,
these data were just various probabilities, and so they never exceed