Pretty interesting, but i dont think its gpuz doing anything wrong, its simply reporting what it sees happening. Both of you have those lines across the voltages so this may be a case of gpuz picking up on voltage fluctuation cause you both are at 12.3 too, which is real close to out of spec, that would be 12.4. You may be witnessing the psu, mobo or gpu trying to smooth that voltage out maybe. It MAY even be picking up on the PWM intervals.
I just checked mine and it has the same thing across only the voltages. Im on GPUZ 2.57.