Region Monitoring not triggering when iPhone screen is turned off

Question

I am using an iPhone5s with IOS 7.1 for testing. I use the locationManagerDidPauseLocationUpdates delegate to call a method to set up the geofence.

- (void) monitorForDepartureFromLastKnownStoppedLocation:(Locations *)lastKnownLocation
{

    CLLocationCoordinate2D lastLocation = CLLocationCoordinate2DMake(lastKnownLocation.latitude, lastKnownLocation.longitude);
    CLCircularRegion *region = [[CLCircularRegion alloc] initWithCenter:lastLocation
                                                                 radius:300          
                                                             identifier:@"departure from last stopped location"]; 
    region.notifyOnEntry = NO;
    region.notifyOnExit = YES;        

    [monitorSignificantChangeObject.locationManager startMonitoringForRegion:region];       
}

This then calls the - (void) locationManager:(CLLocationManager *)manager didExitRegion:(CLRegion *)region delegate method when the user exits the region.

Everything works in the following scenarios.

• app in foreground.
• app in background.
• screen locked with app in background or foreground.

It does't work correctly in the following scenario:

The geofence has been exited (ie didExitregion should fire) and the screen is locked AND the screen is turned off (ie screen is black, this happens a couple of seconds after screen locks) in this scenario the didExitRegion does not fire at all. However as soon as I press the home button the screen comes on (still locked) the didexitRegion immediately triggers.

Is this normal behaviour or am I missing something ?