answer: it jumps back down its own coils seeking circuit "common". Doing so can fry the coils or fry the CDI if the spark jumps back across the primary coil. Same thing came happen with a bad plug too (not just dirty but truly bad so that it won't let the spark jump its gap). So any time the bike won't start you should first pull the plug, hold it to the head fins, and see if you get a spark by pushing the bike or spinning the rear wheel. Weak sparks are really hard to see in broad daylight. Also sparks that you can see will lose strength once the engine is reassembled because high cylinder pressure makes it harder for the spark to jump the gap. Don't ask me why.