This may be related to #3016.

As I understand it arr.contains(item) is implemented as (arr == item).any().

Due to spurious broadcasting this leads to

[5] in array([None, 4, [5]) -> False

and

[5] in array([None, 5, [4]) -> True

Surely, that can't be right.

I'm on Python3.6 and numpy1.13.