android - When opening my app from the recent tasks then it is showing old activity which is already finished? -

in android app opening activity a (which not launcher activity) when user clicks on push notification flags intent.flag_activity_single_top | intent.flag_activity_clear_top , there open activity b , finishes activity a.

now when user presses on activity b activity present in backstack app gets exited. when user clicks on recent tasks , opens app still opens activity b why happening because according me no activity present in backstack splashscreen (default launcher activity) should gets opened up.

i think there big part missing puzzle.