I just bought this house and I'm replacing a fixture in the ceiling, controlled by a wall switch. It's old and doesn't match the style of the other, newer fixtures. Plus it doesn't have a bulb so its time for it to go. I replace the fixture with a new one and screw in a new incandescent bulb. When I flip the switch, the bulb shatters. I'm thinking its a defective bulb, so I put a new bulb in its place and flip the switch. Same thing happens. Its highly unlikely that that 2 bulbs are defective, so I install the old fixture with a working bulb from another fixture. When I flip the switch, the bulb shatters. Just to be sure, I install the new fixture in another room with a new bulb and everything works as expected. At this point, I think I have eliminated the fixture and bulb as the source of the problem. Then I test the wires in the ceiling box with a voltage sensor. When the switch is off, the neutral (white) wire is hot (i.e. live with voltage). When the switch is on, both the neutral and line (black) wires are hot. When I turn off the circuit breaker for this room, both wires are not hot. Any idea what is causing this? I am not afraid to work with electrical wiring, so I am hoping someone can tell me how to fix it.