behaviour matrix depends on how it is created

In Python3 (and in Python2) the behaviour of a matrix depends on how it is created. If elements are assigned directly, it behaves as it should, but if a row is created and then several of these rows are appended to the matrix, this matrix misbehaves, even when it appears to be the same matrix as the first one.
I have added a .py program that shows the bug: codevierkant_experiment.py.
The same happens in Python2, and also in the newer Python3 in Ubuntu 19.10

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: python3 3.6.7-1~18.04
ProcVersionSignature: Ubuntu 5.0.0-37.40~18.04.1-generic 5.0.21
Uname: Linux 5.0.0-37-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.9
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Jan 16 10:17:39 2020
InstallationDate: Installed on 2019-09-05 (132 days ago)
InstallationMedia: Ubuntu 18.04.3 LTS "Bionic Beaver" - Release amd64 (20190805)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=nl_NL.UTF-8
 SHELL=/bin/bash
SourcePackage: python3-defaults
UpgradeStatus: No upgrade log present (probably fresh install)