I am far from certain that it is a bug and that it is in the game itself.
This is the only time I have had trouble with saved games. Then again it is the only career I have played so far into. And too... there was a mod involved that I put into play and took out again..so who really knows...????
Take heart that it is the rarity of the occurance that made it so dog-goned conspicious...
You might well play a whole career without a mishap. i would not sweat it.