Long time ago when I got APM2.5. I found it behavior is wired. Sometime the horizontal line is spin. First I think it came from some of my quad component or firmware. So I leave it on a table.
Last month. I decided to take a look and find a way to fix this. I call my local dealer and ask for support. They told to send it back for service. After investigated, they found a MEMS sensor is damage and need to replace with some cost ($).
Now its return to me. And I feel confident to fly it again. This will make me busy and a lot of fun. :-)
Update 1: I believed that I got defect unit since beginning. Because its flying behavior really good.