Yeah, I had a fly-away with my Spark.
Luckily I was already a little experienced in ATTI flying, and was able to wrestle my Spark to the ground.
In my case it was also a compass error conflicting with the GPS and my stick push (which combined caused a fly-away), then aggravated when I hit RTH (which caused a spiral)
I cancelled RTH, which stopped the spiral, and I forced my Spark to land using the controller.
Back home I did a "factory reset" on the Spark and a fresh calibration.
Problem went away.
Not sure what the issue is.