Have this exact same issue too. Re-signed my CM, who wanted a promise to play as a BBM. I obliged since he had been playing in that role for 2 years at that point. After his contract renewal he played all but one match in that role, with the only exception being a substitute appearance has a SS. After being promoted in back to back years (despite being relegation favourites), he is now upset. Worth noting, I am on his favoured personal list, which seems to be helping somewhat as he hasn't tried to force a move out yet.