We've seen Grimes play alongside a variety of central midfielders under a variety of coaches during his near decade here, and in the entirely of that time we've seen this mythical, forward facing, creative dynamo for about a season and a half in total.
Grimes is hardwired to be cautious and defensive. That's just the way he is. It's got nothing to do with worrying about babysitting the back four. His natural instinct is to play that way, and most managers have indulged him in it.
So far only Potter and Duff have managed to coax any kind of consistently attacking performances out of him. His performances early last season were probably the only bright spot of Duff's entire tenure.