python numpy vectorize duplicated

In my python 2.X/3.X code, I am mapping an array arr using a function func, so I do

def func(i):
    ....
    print(o)
    retu o

output = numpy.vectorize(func)(arr)

When I look at the printout, the output of the first element is printed twice! Has anyone else seen that behavior? Is that bug?

Thanks.