I see the first issue now and I agree that Python behaves strangely.

Numpy
=====

>>> x = array([1,2,3])
>>> x[1:2] = [1,2,3,4,5]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: cannot copy sequence with size 5 to array axis with dimension 1


Python
======

>>> lst = [1,2,3]
>>> lst[1:2] = [1,2,3,4,5]
>>> lst
[1, 1, 2, 3, 4, 5, 3]