problem with FancyArrow overhang

Hello list -

I am trying to use FancyArrow to draw an arrow with given length.
The length I use is from 0 to 100.
I specify length_includes_head=True.
This works fine when I specify a width and length.
But when I specify an overhang, the length of the arrow becomes much longer than 100.
Am I using overhang incorrectly?
Here’s a script with the problem:

from pylab import *
from matplotlib.patches import FancyArrow

ax = gca()
a = FancyArrow( 0, 40, 100, 0, length_includes_head=True, head_width=5, head_length=5)
b = FancyArrow( 0, 60, 100, 0, length_includes_head=True, head_width=5, head_length=5, overhang=5)


Thanks, Mark