In Windows, I noticed that if I don't have any relevant VFs for the book that's open, Logos correctly tells me so:
Yet, it is blue as if it's turned on.
But if I create a temporary one just long enough to turn the VF button off, then delete the VF, the button shows up as off.
I'm going to guess this is expected behavior (the toggle goes to the last status) but my obsessive nature wants to shut something off if I'm not using it.
What's interesting to me, though, is that if @Aaron Hamilton is correct (he usually is :) ) in this thread:
Then the Windows and Mac versions work differently.