Bootstrap columns is consistently buggy for me in Codebits. I've demo'd it for my classes dozens of times--sometimes it works, sometimes it doesn't. Sometimes it works one day, and the same code doesn't work the next, or vice versa. I've even deployed the code in several cases to ensure that it's working correctly and not an oversight on my part. We use codecademy in the classroom and it's very frustrating to show the kids how to do it only to see that it doesn't work in the codecademy viewer-- most frustrating is that they don't get the feedback of seeing whether their code works or not.