When the EMDK library is not used the activity that is started with the action button will spawn a new task which is accessible in the task switcher. This is enabled by the android:documentLaunchMode="intoExisting" property. With the EMDK the activity will be opened in the current task.
Remove the <uses-library> tag in AndroidManifest.xml to make it work again. On all other devices/emulators tested it works without modification.