MnH, I sent you sitemail on this in more detail, but in short, I agree that something should be tweaked. Simply: If a starter that isn't starting the next game has a use-as-reliever option set, then that starter should be ranked higher than a mopup pitcher. I would expect that the starter in that situation would be equivalent to say, a Long B.
In that case, if the game gets close, the mopup should be pulled in favor of that starter, just as if there was another pitcher available in the pen that was set at long B.
I realize that a manager could cause the same behavior to occur by simply putting that starter in the bullpen with a Long B setting, but that would mean that the manager has to micromanage the team on a game-by-game basis. That shouldn't be necessary. This tweak should be made, and I think it would be easy to do.