KK 2.1.5 board autoarms and also does not arm sometimes

It's really scary sometimes when I plug in the battery to adjust some settings and it arms. Why does it do this? Also, sometimes it won't arm until I unplug and replug the battery. It still beeps when I push the throttle to disarm it, it just won't arm.

I usually just ignored the auto arming and turned it off using the transmitter, but I figured I really needed to find a solution after the tuning incident. I was super lucky when I plugged in the battery and sat down to adjust some settings and it autoarmed. I turned to my right to the transmitter by my side to disarm it and the throttle was not all the way down. Heard a whirring, looked back and the quad wasn't there. Looked up, and it was 100 ft in the air. Tried a controlled landing but wind crashed it through a nearby pine tree and miraculously turned out unscathed hanging on the lowest branch. Escaped with all body parts and quad parts intact! One of the scariest moments in my life.

yikes ! Firstly, take your props off until you've got this sorted !

I'd check in the receiver test menu. Yaw, roll and pitch should all read zero when the stick is centered and +/-100 at full travel - especially yaw since that's used for arming and disarming. You may need to change the subtrims and end points in the transmitter to achieve this.

Throttle should read 'idle' and 0 at the bottom (and I've allowed a little leeway on mine, need to move it a little way before it becomes non-zero) and 'full' somewhere between 90 and 100 at the top.

If those are set, then the receiver test menu gives you a mock 'arm' and 'disarm' notice for left stick bottom-right and bottom-left

HI also look in the menu there is an auto arm for planes , make sure its set to stick to arm this is for quads and there is a motor spin on arm turn this off too

Also check that if you have it arming on aux that the arm switch is not flipped, I think I had this happen to mine (scared me to death haha), it was due to having a stick plugged into the aux channel.