Weird fault in Xmas meteor light tube.

I just received a set of cheap (but surprisingly well built) LED meteor lights which I bought on ebay recently. I had them running for a while and then noticed that one of them was doing a very weird multiple echo pattern. At first I though the processor had crashed or glitched and lost track of the effect, but then I realised that it could possibly be a shorted LED bridging two matrix lines together. Resetting the effect didn't help, so it almost certainly is a duff LED causing the weird ghosting.
These effects tend to use tri-state multiplexed LEDs, otherwise known as Charlieplexing. This involves using the matrix lines in three states. Positive, negative or floating. It means that only one LED can be lit at a time, so for multiples they have to be scanned quickly to make them appear lit continuously. The upside is that you can drive a HUGE number of LEDs with just a few lines. You can work out how many by multiplying the number of control lines by the same number minus one. So for five lines you multiply five by four to give control of 20 LEDs. With eight lines you could theoretically control 56 separate LEDs (8 x 7).
I've never come across a Charlieplexing fault before, so it's quite intriguing. It means I have one dead LED that has effectively shunted out its partner LED (in reverse parallel), but the visual effect actually looks quite interesting.