The pix below pretty much tell the story. I looked at the CPU history recently and pix #1 showed a long segment of "computer off". That's not the actual history. I closed the NIS window, then later opened it up again and looked at the CPU history again, and it showed the correct, actual CPU history (pix #2). Bug?
And I subsequently was able to reproduce the anomaly, but not consistently. You may have to close it and open it up again a number of times before the CPU history changes.