Why doesn't my commentThread call give replies for some comment threads?

I have a problem with a commentThread API call. Here is one specific case: comment id: z13ocxipdz3hwxqqe04cgbuadtmnhhmybyc0k

https://www.googleapis.com/youtube/v3/commentThreads?id=z13ocxipdz3hwxqqe04cgbuadtmnhhmybyc0k&part=snippet%2C+replies&key={YOUR_DEVELOPER_KEY}&alt=json&order=time

There are 44 replies for now.

But if you use video_id (not comment id like we did above. Link: https://www.googleapis.com/youtube/v3/commentThreads?videoId=Ui-ulCWmpOU&maxResults=100&pageToken=ChYQp7fipbfsxgIYkNGqiobjxQIgACgDEhQIABCQ0aqKhuPFAhiMqqKive-5AhgCIKwC&part=snippet%2C+replies&key={YOUR_DEVELOPER_KEY}&alt=json&order=time) and come across the comment (you may have to use pageToken to iterate over pages) you will see this:

(Screenshot: https://www.dropbox.com/s/d4bf9tk51eaw7dr/Screenshot%202015-07-21%2021.08.31.png?dl=0)

As you noticed; there are 39 replies (comments) which is not true. And even if we have replies; there is no replies section. Am I missing something?

Why don't the number of replies match?

Why is it that commentThread doesn't have replies even if the video shows it has 39 replies?

Notes: As part I am using 'snippet, replies'. I don't get any API error (like throttle or limit violation)