"Instagram’s developers have decided to layer each tab change on the back stack of the app so that pressing the back button navigates back through the tabs you’ve previously selected. It instantly feels unfamiliar and you’re not sure when the app will let you exit it completely. This fake back trail continues until you hit the home tab where you entered the app and then the back button let’s you exit the app."
Well, isn't that a guideline for Android applications?
[spoiler] http://developer.android.com/guide/topics/fundamentals/tasks... [/spoiler]