Angst (sorry the 1st time), here's where we differ on opinions. You're basically acknowledging that there's a difference in the ball now with negative weight, as compared to when it had positive side.
When the ball had positive side, the ending CG/heavy spot, was on the righthand side of the ball. Now, with negative weight, the ending CG/heavy spot is on the left hand side of the ball.
Whether the ball has a hole in it or not, don't you think the ball will react differently because the weight is on a different side of the ball now..? The ball is reacting differently, not because of the hole, it's because the ending weight/CG is in a different location.
If the ball had a hole, in the position you put it to get 3/4 negative, but still had 3/4 positve side, do you think the ball will roll like it had negative weight, because the hole is the same place it was in the negative side ball..? =:^D