in both situations (smart and dumb nodes), the leds are controlled by pulse width modulation, so there is no reduction in voltage. when it's on (even for a fraction of a second, it's full on, and when it's off, it's full off. The only thing that changes is the duration.
so, now that a lot of ideas have been thrown around, and lots of things have been tried.... does the first node still act up, or does that still happen now? (your original problem?)