Last I heard, they are still in production for that episode. However, I did hear Adam Savage say that they would not use this incident in any way to drum up interest in that episode whenever it does air.

So far, the best explanation I can find of what happened is that unanticipated muzzle lift caused the shot to go awry. Instead of burying itself in the dirt berm, the cannonball careened up and over the berm and downrange hundreds of yards to that neighborhood.

Considering that they had already reportedly fired this cannon 50 times for other episodes, this muzzle lift must have really come as a surprise to the crew. Not that that excuses what happened, of course.