Puzzling behavior with REORDER_TO_FRONT

Activity A starts activity B with no flags. The stack is now A-B with B on top. B starts activity A with FLAG_ACTIVITY_REORDER_TO_FRONT (the only flag). I would expect the stack to now be B-A. However, when the back button is pressed at this point it returns to the home screen. Here I would expect Activity B to be brought to the front. Upon clicking on the launcher icon again, the app opens with B as the running activity and nothing in the stack.

Launchmode is standard (default) in the manifest.

Is this the expected behavior and I'm just not understanding it properly?

EDIT: I have created a test project with no confounding factors and still see the same behavior. I just don't understand it, it doesn't seem to be per the documentation.

EDIT: To me this behavior seems to be a BUG in the framework, see my comment on answer below. I need a workaround.

public class MainActivity extends Activity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


@Override
public boolean onCreateOptionsMenu(Menu menu)
{
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
public void onClickBtn(View view)
{
    Intent flowIntent = new Intent(this, SecondActivity.class);
    startActivity(flowIntent);
}


}

public class SecondActivity extends Activity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
    }

@Override
public boolean onCreateOptionsMenu(Menu menu)
{
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
public void onClickBtn(View view)
{
    Intent flowIntent = new Intent(this, MainActivity.class);
    flowIntent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
    startActivity(flowIntent);

}


}

Manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android&quot;
    package="com.example.tester"
    android:versionCode="1"
    android:versionName="1.0" >
 <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />
    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.tester.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
         <activity
            android:name="com.example.tester.SecondActivity" />
    </application>
</manifest>