Ah it's the fragments that are causing this. Thanks for the info. Would be nice if the back button wasn't default based to fragments but actual URLs (fragments don't get sent to the server, right?).
Fragments indeed don't get sent to the server, and are usually used to track your location inside the document (be it jumping to section headers, or using js-generated dialog boxes, etc.). In an ideal world, this fragment is not changed unless the user explicitly changes the state. Unfortunately, apps often use it to store their own state.
It's possible to avoiding creating history entries by using