I don't know if this is a known bug or something, but if you close Apps like you normally do on Windows 8, they don't close in 8.1's Preview, they're still active in Task Manager. So how can I close them like I did in Windows 8 besides the Task Manager?

Just wanted to state that this is also happening to me, I wanted to verify.  I can close the app by Windows Key + Tab and right-clicking + close but the task is still running when checking task manager for metro apps.

Same here, how I found this thread. drive me bananas.

Hi,

After an app has been closed by the user, it's suspended and terminated, entering the NotRunning state within about 10 seconds. If an app has registered an event handler for the Suspending | suspending event, it is called when the app is suspended, Windows attempts to keep as many suspended apps in memory as possible. By keeping these apps in memory, Windows ensures that users can quickly and reliably switch between suspended apps. However, if there aren't enough resources to keep your app in memory, Windows can terminate your app

Application lifecycle (Windows Store apps)

http://msdn.microsoft.com/en-us/library/windows/apps/hh464925.aspx