I'd say it the other way around : 1/ it's amazing that a code that is used in countless occurences can still have a bug; 2/ (I've studied sorting algorithms for a while) finding such a bug is very clever... Kudo's to the authors.
What's amazing is how little understanding we seem to have over such critical widely-used code. Java opted for a complex and arguably unproven algorithm, so it was always a risk. We now have functional languages that are able to express provably correct sorting algorithms, so the bar is getting higher.
