memory leak in #autoreleasepool block - ios

Question

I use Xcode 4.4 and I develope app for iOS 5.1 with ARC. I have a thread (other than main) that invokes periodically method below.
- (void)updateLabels:(NSTimeInterval)timeSinceLastUpdate
{
int lastTime = self.time;
self.scoreScale -= ((self.scoreScale-1)/5);
self.time -= timeSinceLastUpdate;
if (self.time <= 0) {
self.time = 0.0;
}
if (lastTime != (int) self.time) {
self.timeChanged = YES;
}
#autoreleasepool {
NSString *timeString = [NSString stringWithFormat:#"%.2d:%.2d",(int)(self.time/60),((int)self.time%60)]; //leak!!!
if (self.scoreScale <=1) self.scoreScale = 1;
GLKBaseEffect *scoreValueEffect = [self.sprites objectForKey:#"score_value"];
if (self.scoreChanged) {
scoreValueEffect = [[ILUtils sharedInstance] makeEffectWithString:[NSString stringWithFormat:#"%#",self.score] alignment:UITextAlignmentLeft fontName:#"WetLetters EFN" fontSize:20 withViewSize:self.view.bounds.size withRect:CGRectMake(935, 50, 100, 30)];
}
scoreValueEffect.transform.modelviewMatrix = [[ILUtils sharedInstance] setupSpriteModelviewMatrixWithViewRect:CGRectMake(955, 46-(30*self.scoreScale-30)/2, 100*self.scoreScale, 30*self.scoreScale)];
[self.sprites setObject:scoreValueEffect forKey:#"score_value"];
if (self.timeChanged) {
GLKBaseEffect *timeValueEffect = [[ILUtils sharedInstance] makeEffectWithString:timeString alignment:UITextAlignmentLeft fontName:#"WetLetters EFN" fontSize:24 withViewSize:self.view.bounds.size withRect:CGRectMake(955, 75, 100, 30)];
[self.sprites setObject:timeValueEffect forKey:#"time_value"];
}
}
}
When I use Instruments I can see that memory usage increases in time. When I comment out line creating string memory usage is stable. I also tried to create string with alloc & init methods, but it didn't helped. I've found similiar thread in https://stackoverflow.com/questions/ask?title=#autoreleasepool%20not%20working but enabling/disabling NSZombieEnabled option makes no difference.
I can't figure out why all these strings are not deallocated though I use #autorelease block as said in https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmAutoreleasePools.html.
Did I miss something?
Thanks.
//EDIT
Stuff invoked by makeEffectWithString:
- (GLKBaseEffect*)makeEffectWithString:(NSString*)string alignment:(UITextAlignment)alignment fontName:(NSString*)name fontSize:(CGFloat)size withViewSize:(CGSize)viewSize withRect:(CGRect)rect
{
GLKBaseEffect *effect = [[GLKBaseEffect alloc] init];
effect.texture2d0.enabled = YES;
effect.texture2d0.name = [self textureWithString:string dimensions:rect.size alignment:alignment fontName:name fontSize:size].name;
effect.transform.projectionMatrix = [self setupOrthoProjectionMatrixWithViewSize:viewSize];
effect.transform.modelviewMatrix = [[ILUtils sharedInstance] setupSpriteModelviewMatrixWithViewRect:rect];
effect.useConstantColor = YES;
effect.constantColor = GLKVector4Make(0.7f,0.7f,0.7f,0.7f);
return effect;
}
- (GLKTextureInfo*)textureWithString:(NSString*)string dimensions:(CGSize)dimensions alignment:(UITextAlignment)alignment fontName:(NSString*)name fontSize:(CGFloat)size
{
UIFont *font = [UIFont fontWithName:name size:size];
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
CGContextRef context = CGBitmapContextCreate(nil, dimensions.width, dimensions.height, 8, dimensions.width, colorSpace, kCGImageAlphaOnly);
CGColorSpaceRelease(colorSpace);
CGContextSetGrayFillColor(context, 1.0, 1.0);
UIGraphicsPushContext(context);
[string drawInRect:CGRectMake(0, 0, dimensions.width, dimensions.height) withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:alignment];
UIGraphicsPopContext();
NSMutableDictionary *options = [NSMutableDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:GLKTextureLoaderOriginBottomLeft];
GLKTextureInfo *texture = [GLKTextureLoader textureWithCGImage:CGBitmapContextCreateImage(context) options:options error:nil];
CGContextRelease(context);
return texture;
}
//EDIT
- (void)drawSpriteUsingEffect:(GLKBaseEffect*)effect
{
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 20, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, 20, BUFFER_OFFSET(12));
[effect prepareToDraw];
glDrawArrays(GL_TRIANGLES, 0, 6);
}

Answer 1

You can use the Allocations instruments to "Mark Heap". This seems to have some instructions on how to debug such memory issues.