I just stumbled about an issue in my app: I tested the `didReceiveMemoryWarning` calls to an `UIViewController` including the follow-up calls for `viewDidUnload`. 

This used to work fine in older versions of my app, but was not working now within iPhone Simulator: 
`didReceiveMemoryWarning` was just not called any more.

This was caused by calling `[NSNotificationCenter defaultCenter] removeObserver:self]` in `viewWillDisappear` (self being the UIViewController) to unregister for some lifecycle notifications I did add in `viewDidAppear`.

That global `removeObserver:` call did not only remove my added notifications, but apparently also the system's UIApplicationDidReceiveMemoryWarningNotification notification caused the UIViewController's `didReceiveMemoryWarning` being called.

Is this behaviour by design? I could not find a reference/document which was pointing out, that calling `removeObserver:` within a UIViewController breaks the standard memoryWarning handling.