Nope, not a bug.
I changed an actor's max level to 80, started a new game, enquired on the max level, and it gave me 80.
Any chance you had an actor with 99 max level, played a bit and saved your game, then adjusted it to a different figure? A lot of actor details are set when the actor is added to the party, and are then kept in the save file, so if you change it and load a saved game, it gets the value from the save file and not from the new database settings.