I upgraded my phone to Denim and win phone 8.1 whenever it was released about a week ago. Ever since then some apps aren't closing. Most notably is facebook but that might be because I use it more often than other apps. If I'm in facebook then click on the back button it takes me to the home screen. If I long press the back button I can see facebook is still running. The win phone 8.0 would always close it out. Is this a bug in 8.1 or is it designed to work this way with the new OS?