Something might be slightly off with the running in the background bit, when the "Resources Gained While Away" window pops up it turns off all of the reactor modules. =)
Update: It was doing it with consistent repeatability, but now it's not, but I haven't refreshed the page since. Will keep an eye on it.
Update2: okay, I'm not sure how much leeway there is, but it seems like if your Void Power Generation per second is not far above your consumption (example, I currently have it operating at around 2 void power generated per second more than is being spent) and the reactor modules get turned off when the window pops up