Question [Q] Apps Still Run After Exit Using Back Button CM 7.1

I'm still running the supposed to be stable version CM 7.1 for SGSII and so far, everything is great except for the problem that when I exit an application using back button, the application still remains running in the background (including settings, theme chooser and about everything else I didn't exited using the in-app exit option). I'm using ES Task Manager to verify and kill the running applications. If I failed to do so, the apps continue to run in the background and eats up extra battery. What I want to know now is that, is this the default behavior of CM7? Or did I miss setting something so that when I exit an application using back button the application is actually really being terminated? I know the setting wherein long press on back button to terminate the app but I really want to set the exit using single short press in back button. Any idea? Thanks in advance..