Ios – Removing MKMapView Annotations causes leaks

I've boiled a very complex set of web services and searches down to the simple following code.
I need to be able to add annotations to a map in response to a search (or in the sample below to the click of a button), then allow the user to click the button again and get a new set of results. In reality there will be a different number, but in the simplified example, we always add one annotation to the mapview.
I believe my code should remove the existing annotations and add a new one, but it leaks 32 bytes on second and subsequent button pushes.
What am I missing ? (Or retaining as the case may be!)

testViewController.h

#import <UIKit/UIKit.h>
#import <MapKit/MapKit.h>
#import "MyMark.h"

@interface testViewController : UIViewController  {
    MKMapView *mapView;
}

@end

testViewController.m

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {
    if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) {
        // Custom initialization
        self.title=@"test";
    }
    return self;
}

- (void) storeLocationInfo: (CLLocationCoordinate2D) loc title:(NSString *)t subtitle:(NSString *)st index:(int)i {
    NSArray * annotations = [mapView annotations];
    [mapView removeAnnotations:annotations];

    MyMark * mymark=[[MyMark alloc] initWithCoordinate:loc];
    [mapView addAnnotation:mymark];
    [MyMark release];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    UIBarButtonItem *barButton = [[UIBarButtonItem alloc] initWithTitle:@"Add point to map" style:UIBarButtonItemStylePlain target:self action:@selector(addPushed)];
    [self.navigationItem setRightBarButtonItem:barButton];
    [barButton release];

    mapView=[[MKMapView alloc] initWithFrame:CGRectMake(0.0,0.0,self.view.frame.size.width,self.view.frame.size.height)];
    mapView.showsUserLocation=FALSE;
    mapView.delegate=self;
    [self.view insertSubview:mapView atIndex:0];
    [mapView release];
}

- (void) addPushed {
    MKCoordinateRegion reg = mapView.region;
    [self storeLocationInfo:reg.center title:@"price" subtitle:@"title" index:1];
}

- (void)dealloc {
    [super dealloc];
}

MyMark.h

#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>


@interface MyMark : NSObject<MKAnnotation> {
    CLLocationCoordinate2D coordinate;
    NSString * title;
    NSString * subtitle;
    int index;
}
@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;
@property (nonatomic, readonly) int index;
@property (nonatomic, retain) NSString * title;
@property (nonatomic, retain) NSString * subtitle;
-(id)initWithCoordinate:(CLLocationCoordinate2D) coordinate;
-(id)setCoordinate:(CLLocationCoordinate2D) coordinate;
-(id)setTitle:(NSString *)t subtitle:(NSString *)st index:(int)i ;

@end

MyMark.m

#import "MyMark.h"


@implementation MyMark
@synthesize coordinate, index;
@synthesize title,subtitle;

-(id)initWithCoordinate:(CLLocationCoordinate2D) c{
    coordinate=c;
    NSLog(@"%f,%f",c.latitude,c.longitude);
    return self;
}

-(id)setCoordinate:(CLLocationCoordinate2D) c{
    coordinate=c;
    NSLog(@"%f,%f",c.latitude,c.longitude);
    return self;
}

-(id)setTitle:(NSString *)t subtitle:(NSString *)st index:(int) i{
    self.title=t;
    self.subtitle=st;
    index=i;
    return self;
}

-(void) dealloc {
    [title release];
    [subtitle release];
    [super dealloc];
}