I have noticed that e.g. Facebook and Instagram use the Android back button so that instead of taking you to the previous screen or out of the app, it takes you first to the top of page (if you have scrolled down). If you then click back again, then it takes you to the next screen or out of the app (as one would expect).
I tried to look in Material Design if this is an Android pattern, because it is quite handy instead of adding "scroll to top" buttons to pages and taking up valuable screen space. It seems that this is not however Android practice, but some companies have implemented this by themselves.
I think the problem with this is similar to gestures, it is not intuitive like "scroll to top" button. And if it breaks the back pattern used everywhere else, it can be confusing to users.
Now I'm wondering if our app should implement this feature. Is it well known or just used in a couple of apps? Have you run into examples of this behaviour? I tried Google-fu, but got nothing.