Place a power generator, and then quickly open the base power report by clicking on a different power generator.

If you then wait for the placed generator to finish building itself, the power report will start blinking random numbers instead of the true GEN/USE values. Closing and reopening the report fixes it.

Good one. I was thinking maybe it was a combination of the delta time fluctuating vs rounding error... but I think there's probably just a bug somewhere in my base manager / grouping stuff. Thanks!