Yes, XML storage doesn't make it possible to store results of previous sessions.
Appart from that, Enhanced User Interface behaves "strange" when switched to XML storage - when a task is started, another instance of it appears in the list (of the tasks, not of the corresponding sessions!). I must admit I didn't explore the problem deeper yet, so I'm not sure if it's a bug or just something caused by the inability to store additional info in the storage - but simply said, XML storage is currently considered just a backup option for avast! Home.