I have setup a reactor to turn on whenever the energy cell next to it diminishes to a certain amount of power. By using a comparator to give off a signal from the cell to a line of redstone that ultimately cuts turns off the redstone torch that is pointing at the redstone port.
See pics for reference:

Try putting a single tile of redstone between the torch and the redstone port. Does that fix the problem? Also, are you sure the signal is reaching the torch? From the picture, it looks like the signal may be dying out before it gets there.

Yes, putting a piece of redstone in between the torch and the port does "fix"(more like a workaround) the problem.
About the redstone dying out? If you look "closely" you can see that WAILA reports a power of 2 on the redstone that is powering the torch, which is also off.

Yeah, vanilla's redstone system is pretty awful, so I wouldn't be surprised if you had to work around it with extra wire. It's probably returning false for weak-powered and instead has hardcoded checks for torches or something.

I might look at it some day, but it's not high-priority, especially since there's a workaround.

Not a big deal... I could set a lot of different ways to turn the power on and off