Not a bug as far as I know. It has always been like that. For hit points you can get to 3x the level, but for the other stats, you will need to bring your level up to at least half of your highest stat (HP) until you are allowed to train it again to max 2x the level. It can be really annoying if you're not careful and will make you pay a lot of reds a lot sooner that you planned.