App stops inconsistently at a call to dispatch_sync()

Question

Possible Duplicate:
App blocks while dipatching a queue

I'm using XMPPFramework, and in its code there's a method like this:

- (NSDictionary *)occupants
{
    if (dispatch_get_current_queue() == moduleQueue)
    {
        return occupants;
    }
    else
    {
        __block NSDictionary *result;

        dispatch_sync(moduleQueue, ^{//IT BLOCKS HERE
            result = [occupants copy];
        });

        return [result autorelease];
    }
}

It gets stuck there inconsistently, not always; the app is not responding, but it's not crashing, so I pause it and I see the thread (Thread 1) has stopped there. If I press play, nothing changes. What is wrong? Any ideas?