Quoted from Damien:
One other thing... I noticed recently that occasionally I will shoot the ball through the "Lock", but it will see it as a hit to the castle. If I'm not mistaken, it has happened one the final shot to destroy a castle the 2-3 times it has happened so far.
I've had this happen once and was going to post about it, but you beat me to it! Mine also happened on the "explode" hit (already opened porticulus). I forget which Kingsman it was.