Earlier quoted context omitted.
It didn't break back. It just hijacked the browser's history by adding a 2nd page load in order to inject the "!#" into the address bar. Pressing back would, as a result, act like the refresh button.
I don't follow you. Changing the functional behavior of the back button _sounds_ a lot like broken.
Back works as expected - it takes you to the previous page you were at. Fragment identifiers don't break the back button. That's all from a user perspective's point of view, which is mostly all that matters in the end.
If you look at this from a technical standpoint, then back is a refresh of twitter.com, yes.