Too ad some background, it is possible to capacitively couple a voltage from the HOT (black wire) to a switched wire, and if the digital voltmeter is a very high impedance it will NOT bleed this off and you will get the 'phantom voltage' reading, I have seen this many times. Also, as noted above, the DIMMER switches with the little green lights will register FULL voltage on the switched wire when the switch is OFF, the green light is turned on by sending voltage through the load. I have accidently been shocked 2 or 3 times when I was told the switch was OFF, so I now check if it is a dimmer switch, I make sure the breaker is turned off.
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Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
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