Not sure about this app doubling steps but IOS's health app allows you to prioritize input sources. I have a jawbone UP and I carry my phone with me a lot while walking. The UP is the primary source and both devices are logging steps, but the phone ignores its input when it is also getting step information from the Jawbone.
Do you have a problem with the UP app thinking you slept twice as many hours as you did? I see that sometimes but the Health app counts it correctly. Health (and MyFitnessPal) are having trouble getting the weight data from my iHealth scale.