I'm really curious to see what exactly happened. Because the failure is clearly, a) very obvious, and b) very widespread, it's not like it's a really subtle issue that only affects systems with some unusual configuration, so it's hard to imagine how it couldn't have been picked up in automated QA testing before the update was rolled out. But it's also hard to imagine that no-one involved does that testing. So it'll be revealing to find out how this happened (assuming we ever do).