You're trying to hack a scene in the window using a reflection node.  Since you're using SuperFly, you're better off setting the scene up with a real glass shader and a background billboard with your image attached.  This will properly show up in any file format from your render.  The purpose of the alpha channel saved in your .PNG is for compositing in a third-party program like Photoshop or GIMP where you insert a separate image in post-work.