The Add content dialog sees your newest content
A folder you just renamed, or an app you just installed, now appears in a playlist's Add content dialog without reloading the page.
Renaming a folder or installing an app and then adding it to a playlist showed you the state of things from before your change, so the folder had its old name and the new app was missing entirely. Reloading the page fixed it, once you worked out that was the problem.
The Add content dialog now picks up folders and installed apps as they are when you open it.