Bug in boxplot ?

Hi,

I just encountered something odd.
I have (with import numpy as n and import pylab as pl) :

x = n.arange(0, 2*n.pi, n.pi/30)
z = n.array([n.cos(x), n.sin(x)]).T
If I draw a boxplot on z :

pl.boxplot(z)
the values z are modified.
Is this a feature or a bug ?

Matthieu