Dave, You were right (again)
"1. When the lure is not moving, the ballast keeps the lure upright, as long as the centre of buoyancy is above the centre of gravity. The tow eye does not play. This is stating the obvious.
2. When the bait is moving, the ballast has to counteract the roll. The roll is caused by the water forces across the back, they impart a side force, causing the bait to roll. Because your bait is now being towed, the lever principle comes into play, force x distance. The roll energy is the force and the distance is from the tow axis to the top of the back."etc etc
I never doubted it mate, but just had to field test them in the real fish world of salt water. In the tub they were going O.K (varying degrees), but out there on the lake, they rolled - I'm thinking the problem is the slope of the head, this (I THINK) needs to be symmetrical and weighted low, as you say, get this right and the rest will follow - have been thinking of Dan's comment, so I am going to try a variation of that as well - I'm not going to let this beat me. We caught fish, but not on the three no swim "swim baits". pete