In Settings --> PHP I've added a include path. It works fine, I can lookup a declaration point from a PHP file and jump to a file inside that include path.
After adding that include path it can be seen in the Projects View, displayed at the bottom with a Library icon. I can browse all files in the include path, very handy. But after a while that tree item is missing.
If I close all open file and open the Structure View (default is closed due to performance drain) there I see the Library icon again, with all the folders and files in the include path.
In my opinion, the Projects View is the logical place for browsing through an include path. But why is it only accessable for a short moment? Am I doing something wrong or behaves PhpStorm just different from what I expect?