When accessing a work item from a collections page like Portfolio Items, the expanded/collapsed state of the list is persisted after closing out the work item. However when performing a similar action from a Custom List app, the expanded/collapsed state does not persist and the list is returned completely collapsed.
Release : SAAS
Component : AGILE CENTRAL
The reason it doesn't work the same is because in the collections pages like Portfolio Items, the application is just popping up an overlay window over the existing list; it's part of the code on the Portfolio Items page itself.
When you view a work item from a Custom List app (or any app that you put on a page from the catalog), you're physically navigating away from that page and opening a FDP editor. Then when you close that detail page, you're technically triggering a refresh of the starting page since the browser is navigating back to its referring page.
Because the Custom List app is based on a different javascript framework than the collections pages, there is no resolution for this difference in behavior.