in case no one signalized this yet here and Jani or other AC makers wouldn't know: many people seem to be having problems with the ESC to motor connectors supplied with the jDrones ArduCopter Kit (checj here or here). I crashed my AC about 4 times before I found the right thread on DIYDrones and found out the cause. Luckily 3 out of 4 of those I flew on very low altitude over grass, so nothing really bad happened (I lost a motor, one arm, upper dome center and a couple of propellers because of this, APM and Oilpan survived).
I think those shouldn't be supplied with the kit as they cause temporary lack of current up to the point when the connection is out for too long and a motor stops in flight, which causes a flip and a crash eventually.
Is the problem officially known already?