I've got a case of the altitude stability blues. Above 200 feet it works perfectly in GPS mode. Flies missions perfectly. Landing it is an adventure. It randomly changes altitude about 20 feet. I have to catch it to avoid a hard landing. I have calibrated everything. And I know these things inside and out. I've fixed about 4 of them. The fact that it acts differently above 200 makes it seem like the throttle cutoff activation is somehow in the mix. I'd blame it on the Naza IMU or compass but it's perfect above 200. I noticed something in the V 1.2 RC assistant software. There is no response from the X1 stick input. A "U" stick changes instead. That version of software also allows you to assign channels to the sticks. I had a hard landing with it two flights ago but there have been trouble free flights since then.