i'd blame that ceramic resistor, or wrong wattage bulbs. possibly also dirty points. Basically the issue is that the coil for the ignition grounds through the brakes. When the levers are released, it's grounded through the brake switches, and the ignition still sparks. When you pull the levers to brake, it breaks the ground and the power instead goes through the brakelight bulb, causing it to light up, and it is grounding through the bulb (and/or rear resistor) and still sparking.
The most common problem this creates is if there's an issue in the bulb or wiring, then it can't ground through the bulb, and pulling the brakes makes spark cut out. It sounds like you've got the revers issue, that it's grounding better through the bulb. This could indicate poor grounds or connections up at the brake switches, or instead it could indicate that it's running better with resistance (the bulb) in the line. This could be the case with dirty points for example, the increased resistance is encouraging power to bridge the resistance of whatever tiny corrosion layer is on the points? Note: i'm being completely speculative here, but it makes sense to clean your points and your connections and grounds.