I hastily upgrade my NAZA firmware not really thinking much about it. But when I got to the field there were all sorts of crazy oscillations. This was with firmware version 4.0.2. I'm assuming the default gains have changes and are probably too high for the QAV400 frame. I'm going to look tuning my gains, but in the meantime I thought it would be useful to go through the process of downgrading the NAZA firmware. This is dependent on what version of the NAZA Assistant you have running. The video explains the firmware downgrade process in detail.