It's not necessarily just bad design.
You have to make allowances for unauthorized modifications.
I once had to reassemble an ancient 220 electrical plug that had just fallen apart due to age. I threw the main breaker to the house and got a screwdriver to tighten up all the connections. Just from habit, I held the tool by its insulated handle and shorted out two connectors to make sure the line wasn't hot. It was. The resulting flash blinded me in the dark, and made a noise like a bullwhip cracking.
It appears a previous tenent had done a little electrical maintenance and by-passed the main breaker box.