I'm assuming this came off of the lap joint on the deans plug? You might consider running a better plug than deans -- something like the big bullets. Deans are good plugs, but there isn't much room to make a strong lap joint there and if you're not making the best solder joints in the world (like pressing down and making a good NOT cold lap joint), then they can easily have high resistance, heat up, and melt off.

Another possibility is that something hit it and it shorted out and popped the solder.