Normally, I thought LEDs had the flat side on the cathode (like the stripe on a conventional diode).
Yesterday I found some (Digi-Key Part P410-ND) that have the flat side on the anode (both in real life and in the diagram on the Digi-Key catalog page).
How common is this?
Like other LEDs, these still have the anode lead longer than the cathode. But once you cut the leads, that feature is of course lost.
Incidentally, these P410-ND LEDs are a high-brightness type that work very well in making POV displays (showing letters in the air as you move it past you). They are quite visible with just 2 mA of drive current.