判断网络状态不准确，请大神帮忙看看为什么？

使用Reachability 3.5 ,测试时候先断开网络，当下判定status 为NotReachable，而当连接网络后status 的返回值为：NotReachable ，具体代码如下：请大神们 帮帮忙看下

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
//开启网络状况的监听
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:kReachabilityChangedNotification object:nil];

self.hostReach = [Reachability reachabilityWithHostName:@"www.baidu.com"] ;

self.isReachable = YES;
switch ([self.hostReach currentReachabilityStatus]) {
case NotReachable:
self.isReachable = NO;
//NSLog(@"notReachable");
break;
case ReachableViaWiFi:
self.isReachable = YES;
//NSLog(@"WIFI");
break;
case ReachableViaWWAN:
self.isReachable = YES;
//NSLog(@"3G");
break;
}
//开始监听，会启动一个run loop
[self.hostReach startNotifier];

return YES;
}

-(void)reachabilityChanged:(NSNotification *)note
{
self.isFirstReachable = YES;
Reachability *currReach = [note object];
NSParameterAssert([currReach isKindOfClass:[Reachability class]]);

//对连接改变做出响应处理动作
NetworkStatus status = [currReach currentReachabilityStatus];

//如果没有连接到网络就弹出提醒实况

if(status == NotReachable)
{
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"网络连接异常" message:nil delegate:nil cancelButtonTitle:@"确定" otherButtonTitles:nil];
[alert show];

self.isReachable = NO;

return;
}
if(status == ReachableViaWiFi || status == ReachableViaWWAN)
{
...
}

}