Ok, here's an odd problem I hadn't expected: up to now I have found 2 LiFePO4wered/Pi units with a defective LED. I just replaced the first one without investigating it thoroughly, but when it happened again, I decided to take a closer look at the problem. Below is a microscope picture of a good LED:

You can see the LED die and if you look closely, even the bond wire. Now, take a look at the picture of the defective LED:

I'm not sure what happened here but there's just no LED die in this LED package! That's the craziest thing ever. How can Lite-On get away with that? I thought they were a reputable manufacturer. I bought a full reel of Lite-On LTST-C190KGKT from Digi-Key, so you'd expect them to be genuine. Anyone ever seen something like this?