I'll have it print out some numbers today (don't know why I didn't think of that last night... too tired), but the way it was behaving certainly seemed as if it were giving absolute screen coordinates.
edit: yup bug in my program

I placed the object at at Game.HEIGHT/2 (768/2), but I need to scale my mouse coordinates because my window size is 640x480, but 'game' size is 1024x768. In other words, my glViewport has dimensions: 640x480 (this part may vary), but my call to glOrtho2D has dimensions of 1024x768 (this always stays the same).