Yes lutach that guy is also using a very long wires but in an airoplane your much less likely to get spikes of back emf from the motor when you try to drive it in a direction that it was not intended.

I think the problem was a combination of using a motor that probably generates a lot of back emf (I doubt schulze test mega usa motors) and your wiring loom being so long add to that the fact your running through a eagletree device that probably adds quite a bit of inductance itself.

Needless to say if i were you running a big ass cap as close to your 18.61 as possible should help protect the esc from these transients that the mega is probably generating.

I would also say looking at the wiring you could easily reduce the length of your wires by half and still have slack.