What CrossRoads is saying is that if you turn off the supply voltage and then put a logic "high" voltage on the data line, that voltage becomes greater than the supply voltage, which is undesirable.
Now whether that is an actual problem is another matter. You can most likely provide some isolation by putting a 1k resistor in series with the data line, physically connected at the first neomatrix device. More importantly would be to arrange your code to ensure that whenever the power to the neomatrix is turned off, the data line is always held LOW, and for good measure, is defined as an input.
The more obvious solution is of course, not to interrupt the power to your neomatrix as there is never any reason to do so. Simply commanding all the LEDs off drops the power consumption to a trivial level.