It’s always a good idea to wire a 1kΩ resistor in series with any LEDs you use in order to limit the current, and this is why:
Usually the resistor just burns out, but this LED was entirely different – it split right in half! I’m still not quite sure why, but Occam’s Razor states that it’s more likely to be a manufacturing defect rather than some new phenomenon.
Thanks to my colleague PAS for bringing this to my attention.