It happens, ggd. I don't know if patience/makeup are the only factors, but the penalty can happen in that case, or at least so, a few seasons ago. (I have sometimes wondered if they are more punitive after a two or more demotions have already occurred recently with a franchise.)
In any case, I'll chip in here again, that if this is a sim, then there should generally be a very quick reinstatement of ratings, after a demoted player is promoted back to the higher level, especially after he is brought up the the big league team (or else, why are players sent to AAA "to improve?").
I recently read about the "impatient" young Ron Santo, who was perhaps promised the job, sent down and was very disappointed, then was brought up. If you ask him, I think he'd say it was a character builder, not something that permanently hampered his career. Thought of HBD. Smirked.