If your target build version is Honeycomb 3.2 (API Level 13) or higher you must put the screenSize flag too, as in:
<activity android:configChanges="orientation|screenSize|keyboardHidden" android:name="YOUR ACTIVITY NAME"> </activity>
because even with the "orientation" flag you app will be killed and recreated again with every orientation change when your app is the active one, either being visible on screen or hidden by the lock screen. This is because the usable screen size, mainly in tablets, actually changes due to the change in placement of the system action bar.