Slight shock after the power is turned off to circuit

Describe what you're calling 'romex'. It's very unlikely what you have there is the same thing considered 'romex' today.

All sorts of ideas. Most likely a miswiring of the circuit such that it's shared with another breaker. Half the leg going to one breaker and the other on another. Usually happens when someone tries tying in another switch or outlet inside an already crowded wall box (or they're just plain stupid).

Test the other breakers to see which one is set up wrong. It may lead to an obvious solution that can be easily fixed.

-Bill Kearney

If the "slight shock" was just a tingle, chances are there's just a little capacitively coupled current from an energized conductor running in close proximity parallel to what would otherwise be considered an "open" lead.

Or, there could be a high resistance path created by dampness or through years of crud film accumulating between an energized circuit and something connected to the wiring you touched.

If the fixture job is already finished, then that's that. But it's always wise to use a test light or voltmeter to make sure things which are supposed to be "off" really are.

HTH,

Jeff

I guess that could be possible, but my experience is that it would take a very large capacitive coupling to do it.

The romex I have has 2 wires in it and the metal casing is used as a ground.

Does the metal casing consist of spiral wound interlocking metal tape? If it does you have armored cable which is commonly called BX.

That ain't romex. It's armored cable (BX).

Or back feeding through a "leaking" neutral and then to ground. In other words, there might actually have some current running through it. In sound equipment it causes a buzz when equipment is plugged into different phases of the breaker box and there is a current between neutrals.