CountDownTimer behaves weird/different the second time i open its Activity - countdowntimer

Question

I have been spending way too many hours on this one. And i just dont get it.
What i want: I have a main Activity (lets call it 'Activity Main') from which i am calling a second Activity ('Activity Timer') that has a CountDownTimer. Upon starting "Activity Timer" i want a Countdown to start running; it is only supposed to play a sound when it finishes. There is also a 'Pause-Button' which pauses/resumes the Countdown. 'Activity Timer' sends back results to 'Activity Main' via Intent when a button is pressed (either 'Success' or 'Fail' - well, it's a game). I am back at 'Activity Main' and all just worked perfectly fine.
That is until i start 'Activity Timer' a second time (for the secound round): The Countdown starts but cannot be paused. It just keeps ticking, even though i cancel() the Countdown and finish() the 'Activity Timer'.
Here's the code:
Activity Timer
public class GameActivity extends AppCompatActivity {
long countdown_time;
Button button_fail, button_success;
ImageButton imgbtn_pause;
boolean cd_running = false;
boolean countdown_auto = true;
TextView textView_countdown;
private static CountDownTimer;
Vibrator vibrator;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.game_activity);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
// Preferences
prefs = getSharedPreferences("shared_preferences", Context.MODE_PRIVATE);
// Intent
Intent i = getIntent();
countdown_time = i.getLongExtra("countdown_time", 60000);
// Assigning
button_fail = (Button) findViewById(R.id.btn_fail);
button_success = (Button) findViewById(R.id.btn_success);
textView_countdown = (TextView) findViewById(R.id.tv_countdown);
imgbtn_pause = (ImageButton) findViewById(R.id.imgbtn_pause);
button_fail.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (cd_running) {
countdown.cancel();
}
cd_running = false;
countdown = null;
Intent returnIntent = new Intent();
if (risk) {
returnIntent.putExtra("result", "-3");
} else {
returnIntent.putExtra("result", "0");
}
setResult(Activity.RESULT_OK, returnIntent);
finish();
}
});
button_success.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (cd_running) {
countdown.cancel();
}
cd_running = false;
countdown = null;
Intent returnIntent = new Intent();
setResult(Activity.RESULT_OK, returnIntent);
finish();
}
});
imgbtn_pause.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (cd_running) {
countdown.cancel();
cd_running = false;
imgbtn_pause.setBackgroundResource(R.drawable.play_2);
} else {
startCountDownTimer();
imgbtn_risk.setVisibility(View.INVISIBLE);
imgbtn_pause.setBackgroundResource(R.drawable.pause_2);
}
}
});
private void startCountDownTimer() {
cd_running = true;
imgbtn_pause.setBackgroundResource(R.drawable.pause_2);
countdown = new CountDownTimer(countdown_time, 1000) {
public void onTick(long millisUntilFinished) {
countdown_time = millisUntilFinished;
textView_countdown.setText("" + millisUntilFinished / 1000);
}
public void onFinish() {
countdown.cancel();
countdown = null;
cd_running = false;
if (!mute) {
vibrator = (Vibrator) GameActivity.this.getSystemService(Context.VIBRATOR_SERVICE);
vibrator.vibrate(1000);
countdown_sound.start();
}
textView_countdown.setVisibility(View.INVISIBLE);
textView_gameOver.setVisibility(View.VISIBLE);
imgbtn_pause.setVisibility(View.INVISIBLE);
}
}.start();
}
The call from 'Activity Main':
#Override
public void onClick(View view) {
Intent i = new Intent(GameMenu.this, GameActivity.class);
i.putExtra("countdown_time", countdown_time);
startActivityForResult(i, 1);
}
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
if (requestCode == 1) {
if (resultCode == Activity.RESULT_OK) {
String result_string = data.getStringExtra("result");
int result_int = Integer.parseInt(data.getStringExtra("result"));
}
if (resultCode == Activity.RESULT_CANCELED) {
// No result
}
}