If you are using my powermeter software in conjunction with Maki's module and have a unstable readings or sporadic extrem value changes, this is a problem of the CS pin. It may be a grounding issue - Makis is currently analysing the problem.
My way to fix it was, to put a 47kOhm resistor at JP1 position. . This jumper is usually not used. Maybe you must fiddle around a little bit with the resistors value.