Q:

iOS UIView inheritance bad performance

I just wanted to do performances test on iOS on my project, and I am a little bit surprised of this behaviour : 
In a simple SingleView Application, if I add 1000 UITextField on rect (20, 20, 200, 200) from the viewDidLoad: main controller method, it works great. It's stupid, but it works.
Now i create my class "MyTextField" inherited from UITextField and that implements drawRect: . The drawRect: implementation does nothing and i'm not overriding any other methods of UITextField. I replace my 1000 UITextField with MyTextField class, and surprise : it crashes. Worse, my iPhone reboots !
I don't understand why. According to the Apple documentation, my drawRect does not need to call super. I also try to call super drawRect: but the result is the same. Reboot due to "Receive memory warning". 
Is there an explanation to this please ?
EDIT : to be clear : 
It crashed (and my iPhone reboots) : 
@implementation MyTextField

-(void)drawRect:(CGRect)rect {
    [super drawRect:rect];
}

@end

It crashed too (and my iPhone reboots) : 
@implementation MyTextField

-(void)drawRect:(CGRect)rect {
    // or does nothing
}

@end

It works : 
@implementation MyTextField

@end

Here is my ViewController :
- (void)viewDidLoad {
    [super viewDidLoad];

    NSLog(@"######### START ###########");
    for (int i = 0 ; i < 1000 ; i++) {
        MyTextField *tf = [[MyTextField alloc] initWithFrame:CGRectMake(20, 20, 200, 200)];
        [self.view addSubview:tf];
    }
    NSLog(@"######### END ###########");
}

It does nothing else

A:

They are warning you that blank implementation of drawRect affects performance
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.

