NSURLProtocol canInitWithRequest: only works for certain requests

I have a WebView that I want to intercept and modify certain requests from various sites. I am doing the exact same modification to each of the intercepted requests regardless of which site it comes from. It works perfectly for every site except one, for seemingly no reason. Here is my code:

In my ResourceLoadDelegate

- (NSURLRequest *)webView:(WebView *)sender resource:(id)identifier willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse fromDataSource:(WebDataSource *)dataSource
{
    //predicates
    const NSPredicate *site1Predicate = [NSPredicate predicateWithFormat:@"SELF like \"/*predicate1*/""];
    const NSPredicate *site2Predicate = [NSPredicate predicateWithFormat:@"SELF like \"/*predicate2*/""];
    const NSPredicate *site3Predicate = [NSPredicate predicateWithFormat:@"SELF like \"/*predicate3*/""];
    const NSPredicate *site4Predicate = [NSPredicate predicateWithFormat:@"SELF like \"/*predicate4*/""];
    const NSPredicate *site5Predicate = [NSPredicate predicateWithFormat:@"SELF like \"/*predicate5*/""];

    //predicate arrays
    const NSArray *songPredicates = [NSArray arrayWithObjects:site1Predicate, site2Predicate, site3Predicate, site4Predicate, site5Predicate, nil];

    //site is an int with its defined in an enum
    if ([[songPredicates objectAtIndex:site-1] evaluateWithObject:request.URL.host])
    {
        NSMutableURLRequest* newRequest = [request mutableCopy];
        [InterceptionProtocol setProperty:self forKey:@"MyApp" inRequest:newRequest];
        dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            /* Do stuff */
        });
        return newRequest;
    }
    return request;
}

In InterceptionProtocol.m

+ (BOOL) canInitWithRequest:(NSURLRequest*)request
{
    id delegate = [NSURLProtocol propertyForKey:@"MyApp" inRequest:request];
    if (delegate) NSLog(@"Can init: %@", request);
    return (delegate != nil);
}

For some reason this works perfectly for everything except site 4. I have stepped through the code and I know that the predicate is matching correctly. I do not know how this could work for the other sites but not this one. Any ideas?

Edit

Full source code can be found here: http://github.com/garrett-davidson/iLikeMusic