Crash when calling get_shape(<array>) from FrameExractor

Here is an example that leads to the crash, as posted to bob-devel google group:

from bob.ap import *
from bob.io.audio import *

read = reader('test.wav')
data = read.load()
signal = data[0]
fe = FrameExtractor(
    sampling_frequency=48000,
    win_length_ms=20,
    win_shift_ms=10,
    normalize_mean=False)
shape = fe.get_shape(signal) # <= Here it crashes