Hi everyone,
I experienced a ‘funny’ problem this weekend and am lost as to what could be happenning…so I thought I’d ask the experts 
To give some context, I am flying a 450 frame with an APM2.5, 1000KV motors, 10 inch props and 30A SimonK ESCs…pretty common setup.
So far so good…I had to fiddle around a bit to get the gains right but it flies great now.
Last weekend it was slightly windy in my hometown. However I had been grounded for some weeks and decided to go for a fly anyway.
Once airborne I couldn’t do much but fight against the wind in AltHold mode. The quad did pretty good but I had to input significant left roll constantly to keep it steady.
After some minutes I decided to land and disarm as I was not having a very good time.
Shortly after the wind seemed to calm down a bit so I decided to go up again.
Upon arming I thought left side motors were turning slightly slower than their opposites. However I raised the throttle slowly and…bam!! the quad tilted left and hit the ground with two arms.
I disarmed and tried again…same result. Reset APM…same result. Disconnect and reconnect the battery…same result. Then decided to go home 
The next day, still a bit breezy, I decided to go out again to find out some more about this problem.
I took off really carefully expecting the quad to tilt as it did last time but this time it went up just fine.
Now I had to fight head wind so I was constantly pitching forward. The quad flew ok.
After a while I decided to land and check if the quad was “misbehaving” again. Unfortunately it did. It would tilt forward upon raising throttle.
It’s like it was still thinking it had to fight against the head wind!! Disarm, re-arm, APM reset and battery recycle didn’t solve the problem either.
So I thought I’d hold the quad over my head to get a feeling of the tilt. To my surprise it wasn’t tilting at all in response to the throttle 
At some point I even released the quad and it started flying level…no idea of how this solved the problem!!
So I flew through the whole battery and then changed to a fresh one. Tried to takeoff from the ground and the forward titlt appeared again…
Had to grab it again and release it by hand…and this worked fine again!!
I haven’t gone through the logs yet but the truth is I don’t even know what I’m looking for.
Anyone has ever seen a similar behaviour? Anything to configure to solve it?
Thanks for reading this far!!