Demonstrates NSURL crash when subclassing, see http://www.openradar.me/9729706

NSURLBug.m

#import <Foundation/Foundation.h>

@interface MyURL : NSURL
@end

@implementation MyURL
@end

void testURL(Class urlClass, NSString *string)
{
	NSURL *url = [[[urlClass alloc] initWithString:string relativeToURL:[NSURL URLWithString:@"http://www.apple.com"]] autorelease];
	NSString *absoluteString = [url absoluteString];
	NSLog(@"[%@] %@", urlClass, absoluteString);
}

int main(int argc, char *argv[])
{
	NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
	testURL([NSURL class], @"iphone");
	testURL([NSURL class], @"");
	testURL([MyURL class], @"iphone");
	testURL([MyURL class], @"");
	[pool release];
	return 0;
}

Looks like the mere use of a subclass triggers the bug. The subclass doesn't need any methods in it. You could trim a few lines, keeping the same main() function:

@interface MyURL : NSURL
@end

@implementation MyURL
@end

void testInitURL(Class urlClass, NSString *string)
{
    NSURL *url = [[[urlClass alloc] initWithString:string relativeToURL:[NSURL URLWithString:@"http://www.apple.com"]] autorelease];
    
    NSString *absoluteString = [url absoluteString];
    NSLog(@"[%@] %@", urlClass, absoluteString);
}