Quoted from Gnatty:
Remove the screw from the metal rail guide that diverts the ball out of the lock. Bend it out slightly so the tab is past the screw hole in the playfield then reinsert the screw in the hole. It will now divert the ball down to the right flipper when locked balls are released. I did this on mine, worked great and no sloppy modification needed.
When I started reading this thread, I was gonna say I've never seen this happen.
My Grand Lizard was Gnatty's, so that probably explains it. It's a good fix - it works!