Read original post by Andreas Hammar at Jayway Team Blog
In Windows 8 Metro apps, the navigation model has been improved over the previous one found on Windows Phone. One difference is that page caching has to be manually enabled for each page, as we explained in part 8 of our Windows Phone to Windows 8 conversion series. And, the page cache is active for both forward and backward navigation, which recently gave me some headaches. The solution is to clear the cache when backing away from the page, and forcing other pages to always be cached.