Question: I have come across a lot of infinite scrolls browsning the web but I have yet to find one that does not break when returning back to the list from for example looking at a newsarticle. What is the appropriate way to deal with the "back" button going back to the list?

In most cases I get to the top of the list and I have to scroll down all over again(loading more and more for each article I watch further down in the list). It can even be so frustrating that I just don't want to browse older articles on mobile devices! (On a desktop I mitigate this issue by opening the article in a new tab)?

Does anyone have an example where this problem have been solved in a ux friendly way? Maybe only load the last chunk the user was actually on? Loading the complete list all the way down to the user's previous position seems rather inefficient.

Answer: 
I think the forum software discourse has a good solution for this.

They are updating the url while you are scrolling down. If you goto to another page from the list and return using the back button, you are at the same position you have left the page.

Try it yourself:
<http://try.discourse.org/>

This blog article has more details of the reasoning behind this and about the implementation:

<http://eviltrout.com/2013/02/16/infinite-scrolling-that-works.html>
You pretty much answer your own question:

* Update the URL to reflect whatever content is being shown

Here's an example: <http://blog.rnf.me/ux-of-urls/#/>.

As you press space bar to move through slides, the URL updates: <http://blog.rnf.me/ux-of-urls/#/19>.

The URL update is also a little delayed so that you don't pollute your Back history too badly. However, for me, I'd like a slightly longer delay.