[Image-SIG] possible bug in OpenCV python module (cv2)

[ha]

When I run:
img = uint8([[0,255,255,0],[0,255,255,0],[0,255,255,0],[0,255,255,0]])
aaa,bbb = cv2.findContours(img,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)
img

I get the following output:
array([[  0,   0,   0,   0],
        [  0,   2, 130,   0],
        [  0,   2, 130,   0],
        [  0,   0,   0,   0]], dtype=uint8)

This does not seem to me as the expected behavior, as the input image
has changed. Should this be treated as a bug?

What's your experience with cv2 module?
Is this the right place to discuss such problems?