I think what needs explained to all of us is how the closer role code is written when the "Use Closer in Save Situations Only" is not checked. There supposedly is some kind of underlying special code written for a pitcher in a closer's role. We all pretty much know when a closer will enter the game when the "Use Closer in Save Situations Only" is checked, but when it is not checked it becomes more unclear.
To me, it seems that there has to be some underlying code written too as to when a closer with a "use closer in save situations only" isn't checked, and my hunch is that the code seems to take precedence over any box that we checkmark.
Whether that is the case or not, I absolutely agree with your position that if you checkmark "Use Mopup Only When Losing", then that should be honored, period. And that's the bottom line here, especially when you have at least one other arm available that could be used before having to turn to a mop up guy. But again, I believe that the closer code used (whether the box is checked or not) is taking precedence, and if so, then this should be better defined or explained to us.