AutoreleasePool not catching breakpoints, no warnings, no reporting in Instruments Leaks

I'm trying to catch scenarios if there is no autorelease pool in place.
This is my test app.

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    [self performSelectorInBackground:@selector(bgOperation:) withObject:nil];
}

- (void)bgOperation:(id)obj
{
    NSString *string [[[NSString alloc] init] autorelease];
}

I've tried setting the breakpoint objc_autoreleaseNoPool.
I've tried profiling with Instruments / Leaks.
OSX 10.7.5 XCode 4.3.3 Targeting 10.6, AutomaticRefCounting = NO, GarbageCollection = Unsupported.

I understand NSApplication includes it's own autorelease pool. But my understanding was that each call to performSelectorInBackground: needed it's own autorelease pool.

Update from the suggestions:
I tried this..
in main.m, no luck.

int main(int argc, char *argv[])
{
    NSString *junk = [[[NSString alloc]init]autorelease];
    return NSApplicationMain(argc, (const char **)argv);
}

And this..
In my appDelegate, also no result.

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    [NSThread detachNewThreadSelector:@selector(bgOperation:)
                             toTarget:self
                           withObject:nil];
}

And this..
With pthreads in my main.m

void *doJunk(void *ptr){
  NSString *junk = [[[NSString alloc]initWithString:@"string with no pool"]autorelease];
  NSLog(@"%@", junk);
  pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
  pthread_t thread;
  pthread_create(&thread, NULL, doJunk, NULL);
  return NSApplicationMain(argc, (const char **)argv);
}

I understand that due to the OS level maybe nothing is leaking (still haven't confirmed), but when I target 10.6 I see a number of "No Pool" messages in the logs. If it only leaks due to the OS level, then I need a way to catch these scenar