Maybe you misread the test kit, or your plants are metabolizing the nitrite instead of the bacteria. How much fish food did you put in the tank? Are you still dosing? Oh, and how densely is it planted?
Byron advised me against doing any sort of traditional "cycling" when I was setting up my current aquarium - the new philosophy I've learned is to plant adequately and see to it that the plants are thriving, and then introduce fish gradually. The plants, when there are enough of them, are so quick at sucking up ammonia/nitrite/nitrate than the you rarely see a ammonia or nitrite spike that you see with traditional cycling methods. The bacterial colonies will eventually develop as well using the "green" method as well, by the way.