When I first started using the new app, any device renamed in the last few days still showed under the previous name. As I'd been swapping the names of devices this was particularly problematic. I also had a shed load of devices that I'd deleted over the last few months - they were maintained dynamically by a parent device handler and were long gone on IDE and in Classic. I deleted them easily enough, though it was tedious. I got the feeling that syncing was mostly only reliable going one way from new to classic.