Well it would have been a problem if anyone connected the supply wires according to the jumper colours. Classic instant darkness device if the lights and sockets are on the same RCD
I found something similar in a friend's kitchen a few months ago. I was called because touching the dishwasher and stove at the same time would cause an electric shock. I tested all kitchen sockets and one of the sockets immediately tripped the RCD as I pressed the "Test" button on my tester. Turns out someone had extended the old live and neutral wires with black and blue but left the red earth. The moron who installed the new socket didn't realise this and connected the socket to blue and red (presumably mistaking red for brown). As far as I know this socket was installed by the cleaning lady's husband.
As there were some other DIY specials the kitchen was entirely rewired.
