AFNetworking setUploadProgressBlock does not lead directly to 100%

I am using AFNetworking Framework to make it easy to upload photos to a website. The loading is working fine, but I need to show the progress in the UIProgressView. The problem is that progress moves from 0 to 100% per second or so after the download starts, and stays at 100% for some time depending on the number of photos uploaded. I am uploading 1 to 6 photos at a time using one request. Any ideas on what's going on here? Does AFNetworking support photo size?
It displays correctly in NSLOG:

2012-04-03 10:49:45.498 PhotoUp[3689:2207] Sent 32768 of 217931 bytes
2012-04-03 10:49:45.499 PhotoUp[3689:2207] Sent 65536 of 217931 bytes
2012-04-03 10:49:45.501 PhotoUp[3689:2207] Sent 98304 of 217931 bytes
2012-04-03 10:49:45.502 PhotoUp[3689:2207] Sent 131072 of 217931 bytes
2012-04-03 10:49:47.795 PhotoUp[3689:2207] Sent 134310 of 217931 bytes
2012-04-03 10:49:49.070 PhotoUp[3689:2207] Sent 136730 of 217931 bytes
2012-04-03 10:49:50.819 PhotoUp[3689:2207] Sent 139150 of 217931 bytes
2012-04-03 10:49:52.284 PhotoUp[3689:2207] Sent 141570 of 217931 bytes

      

        
        
        
      

    

Here's the code:

NSString *numberOfPhotosAsString = [NSString stringWithFormat:@"%d", numberOfPhotos];


NSString *fileBase = @"file0_";
NSString *fileNameBase = @"SourceName_";
NSURL *url = [NSURL URLWithString:@"http://www.mywebsite.com"];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:url];
NSMutableDictionary *params = [NSMutableDictionary dictionaryWithObjectsAndKeys:
                        numberOfPhotosAsString, @"PackageFileCount",
                        wtID, @"wtID",
                        @"PU", @"type",
                        nil];
for (int i= 0; i < numberOfPhotos; i++)
{
    [params setObject:[fileNames objectAtIndex:i] forKey:[fileNameBase stringByAppendingFormat:@"%i", i]];
}

NSMutableURLRequest *request = [httpClient multipartFormRequestWithMethod:@"POST" path:@"/ReceivePhoto.aspx" parameters:params constructingBodyWithBlock: ^(id <AFMultipartFormData>formData) { 

for (int i = 0; i < numberOfPhotos; i++)
{
    // may want to experiment with the compression quality (0.5 currently)
    NSData *imageData = UIImageJPEGRepresentation([images objectAtIndex:i], 0.5);
    [formData appendPartWithFileData:imageData name:[fileBase stringByAppendingFormat:@"%i", i] fileName:[fileNames objectAtIndex:i] mimeType:@"image/jpeg"];
}
}];

AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];

[operation setUploadProgressBlock:^(NSInteger bytesWritten, NSInteger totalBytesWritten, NSInteger totalBytesExpectedToWrite) {
    NSLog(@"Sent %d of %d bytes", totalBytesWritten, totalBytesExpectedToWrite);
    float progress = totalBytesWritten / totalBytesExpectedToWrite;
    [selectLabel setText:[NSString stringWithFormat:@"%d", progress]];
    [progressView setProgress: progress]; 
    //[testProgressView setProgress:progress];
}];
[operation  setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

    [self imageRequestDidFinish];


} 
                                  failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                                      NSLog(@"error: %@",  operation.responseString);

                                  }
 ];