[Nut-upsuser] output.voltage on a CyberPower CP1350PFCLCD

[Weedy]

nut 2.7.2
linux 3.18.7
CyberPower CP1350PFCLCD

The LCD shows the same for input and output, my multimeter also
matches the input voltage.
But nut is giving me different numbers. How do I debug this?

input.voltage: 122.0
output.voltage: 138.0

I still need to check what it does on battery and what the other
readings are. But the voltage stuck out at me.