Why does time based pagination in Facebook GraphAPI return wrong result?

Question

Facebook

Faced the following problem. Using the Facebook GraphAPI, I want to extract all the comments from here for later analysis. There are quite a lot of comments on this post (about 50K). I'd like to be able to send HTTP requests with start_date and end_date parameters in order to be able to retrieve comments for a specific time interval.
Facebook GraphAPI provides the so-called time based paging - you can set the time period with the since and until parameters.
What is the problem
I want to get some amount of comments starting from 2013-08-01 (YYYY/MM/DD date format) in unix time this corresponds to 1375315200. By making the following HTTP request, I expect to receive data that has a created_time field greater than 1375315200 :

curl -i -X GET "https://graph.facebook.com/v2.5/10151775534413086/comments?fields=created_time&offset=0&since=1375315200&limit=5&access_token={MY_TOKEN_HERE}"

However, this query gives me the following result:

{
  "data": [
    {
      "created_time": "2013-07-09T14:17:20+0000",
      "id": SOME_ID_HERE
    },
    {
      "created_time": "2013-07-09T18:03:17+0000",
      "id": SOME_ID_HERE
    },
    {
      "created_time": "2013-07-09T14:13:52+0000",
      "id": SOME_ID_HERE
    },
    {
      "created_time": "2013-07-09T14:22:16+0000",
      "id": SOME_ID_HERE
    },
    {
      "created_time": "2013-07-09T14:13:26+0000",
      "id": SOME_ID_HERE
    }
  ],
  "paging": { CURSORS DATA HERE }
}

The comments I received as a result were made earlier than 2013-08-01, and should be later.
Why is this happening? How can I extract from all the comments on a post only those that fall within the time period specified in since/until ?
I did not find an answer to the question in the documentation ... I found relatively similar problems here , here and here , but this information is useless for my case.
PS Currently using Facebook GraphAPI version 2.5