Are you serious?
You make a point of stating that you are using "Subtract Front Shape" but want the inverse result of what it is correctly producing.
Try the alternative combining-modes!
A path is not a selection but you can change a path into a selection and fill the selection. There is even an icon in the bottom of the paths palette that you can use to make a selection for the path.
What you filled may have been a layer or some other target that fill you used was for. Again a Path is not a selection.