That gets me every time I read in the media about a 'bug' that enabled some complex data transfer. People, somebody has to decide, plan, code, test and deploy the behaviour, and make sure it works. And yet, people accept the explanation it seems without much thought.
The email contacts feature already existed but was disabled in the past, so it just needed to be a Boolean switch. Like anyone who uses Messenger, I can believe they could introduce a regression and never fix it.
