I am certain that this was caused by something I did. I started a new game to test whether I could change the day of month for a new characters birthday. When that was successful I then quit the game. I tried some time later to continue my previous game. I hit 'resume current game', not realizing that the game I never actually played had become the current game. When I saw that it was, I deleted that save and went back to the end of the previous week in the game I had been playing.
This is where the problem arose. Two of my players suddenly had their potentials lowered by 10-40% in their physical skills only. I went back to the week before that, and the potentials were also reduced. The week before that, and again reduced. As near as I can tell the reductions were the same in each case, and they only affected physical skills and long term form (which dropped to around 70%).
These characters have effectively been ruined. Since I was going to start a new game when 1.0c became available, this is not as bad as it could have been, but I would really like to keep it from happening again. Do you have any suggestions?