How can I return to a parent activity correctly?

Updated Answer: Up Navigation Design

You have to declare which activity is the appropriate parent for each activity. Doing so allows the system to facilitate navigation patterns such as Up because the system can determine the logical parent activity from the manifest file.

So for that you have to declare your parent Activity in tag Activity with attribute

android:parentActivityName

Like,

<!-- The main/home activity (it has no parent activity) -->
    <activity
        android:name="com.example.app_name.A" ...>
        ...
    </activity>
    <!-- A child of the main activity -->
    <activity
        android:name=".B"
        android:label="B"
        android:parentActivityName="com.example.app_name.A" >
        <!-- Parent activity meta-data to support 4.0 and lower -->
        <meta-data
            android:name="android.support.PARENT_ACTIVITY"
            android:value="com.example.app_name.A" />
    </activity>

With the parent activity declared this way, you can navigate Up to the appropriate parent like below,

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    // Respond to the action bar's Up/Home button
    case android.R.id.home:
        NavUtils.navigateUpFromSameTask(this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

So When you call NavUtils.navigateUpFromSameTask(this); this method, it finishes the current activity and starts (or resumes) the appropriate parent activity. If the target parent activity is in the task's back stack, it is brought forward as defined by FLAG_ACTIVITY_CLEAR_TOP.

And to display Up button you have to declare setDisplayHomeAsUpEnabled():

@Override
public void onCreate(Bundle savedInstanceState) {
    ...
    getActionBar().setDisplayHomeAsUpEnabled(true);
}

Old Answer: (Without Up Navigation, default Back Navigation)

It happen only if you are starting Activity A again from Activity B.

Using startActivity().

Instead of this from Activity A start Activity B using startActivityForResult() and override onActivtyResult() in Activity A.

Now in Activity B just call finish() on button Up. So now you directed to Activity A's onActivityResult() without creating of Activity A again..

I had pretty much the same setup leading to the same unwanted behaviour. For me this worked: adding the following attribute to an activity A in the Manifest.xml of my app:

android:launchMode="singleTask"

See this article for more explanation.

You declared activity A with the standard launchMode in the Android manifest. According to the documentation, that means the following:

The system always creates a new instance of the activity in the target task and routes the intent to it.

Therefore, the system is forced to recreate activity A (i.e. calling onCreate) even if the task stack is handled correctly.

To fix this problem you need to change the manifest, adding the following attribute to the A activity declaration:

android:launchMode="singleTop"

Note: calling finish() (as suggested as solution before) works only when you are completely sure that the activity B instance you are terminating lives on top of an instance of activity A. In more complex workflows (for instance, launching activity B from a notification) this might not be the case and you have to correctly launch activity A from B.