What's the pin-out on these? Are the two floating pins continuous with each other? It looks like the two pins are connected to the substrate on either side of the chip, while the case is attached to the top contact.
While you can't see the pl520 emitting point, you can guess at where it is and you will notice that the "cavity" is off-center, and can guess that it is under the long strip of metal with the tiny line that runs just off to the side of the number. Likely, the emission point is just under that thin line, on the front surface.