HELP! QAV250 suddenly "punches out" with no input and throttle at zero. Noob here.  I've only had about 3 batteries through my QAV250 build.  Naze32 acro and a Spektrum DX6i.  I have been having a weird control issue lately.  I will be flying normally (trying to get the hang of the quad)(turns are hard/weird), and it will suddenly punch out.  Even if I drop the throttle to zero that doesn't affect it.  The only way I can stop it is to flip my arm switch to kill the quad.  I've had some pretty nasty falls already from this.   
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Earlier today, this happened and after replacing the broken prop, unplugging and plugging in the battery, and turning off/on the controller I set the quad back on the ground.  As soon as I flipped the arm switch the quad took off with the throttle at zero.  This was 5 minutes after I flew around normally for 2 minutes.   

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I really have no clue what to do.  I'm still learning everything.  Any input/advice would be greatly appreciated.  

Thanks guys!