Pressing the back button causes onPause to be called, and the app stays paused until it is re-launched by clicking on the icon, at which point, onDestroy gets called, and the main activity continues to shut down.

Simple class to demonstrate. Note, as far as I can tell, this only happens on the Nexus One. I can't reproduce it in the emulator or on my Droid.

package com.vimtips.testshutdown;

import android.app.ActivityGroup;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;

public class MainActivity extends ActivityGroup {
    private static final String TAG = "MainActivity";
    private int counter = 3;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(keyCode == KeyEvent.KEYCODE_BACK) {

            if(counter-- > 0) return true;
        }

        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onPause() {
            super.onPause();
            Log.d(TAG, "onPause called");
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

        if(isFinishing()) {
            Log.d(TAG, "Shutting down");
        }
    }
}

And here's the log:

I/ActivityManager(  132): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10100000 cmp=com.vimtips.testshutdown/.MainActivity }
I/ActivityManager(  132): Displayed activity com.vimtips.testshutdown/.MainActivity: 305 ms (total 305 ms)
D/MainActivity( 1393): onPause called
I/ActivityManager(  132): Displayed activity com.vimtips.testshutdown/.MainActivity: 302 ms (total 302 ms)
D/MainActivity( 1393): Shutting down

This doesn't appear to happen on a normal Activity, just an Activity group, though looking at Android's sourcecode, I can't figure out why. It's causing some serious problems with my app.

Anyone know why this would happen?