Youtube API Subscription.ContentDetails.NewItemCount returning zero if querying myself but return different value from Google API Explorer - youtube-api

Question

When using the youtube API to get the list of my subscriptions and all the related details I get a number of information from the snippet and contentDetails part of the response object.
When I call the service from my script the contentDetails.newItemCount always return zero, this should indicate the number of new videos on the channel since last time I've opened the channel. The contentDetails.totalItemCount (total number of videos for the channel) is accurate instead.
In contrast if I run the same query through the google api explorer, the same variable contains the correct information and not zero.
The call I make from my PHP script is exactly the same as the one run on the google api explorer so I can't explain or understand why I'm getting different results. The code I use is roughly the following
$this->_youtube = new Google_Service_YouTube($this->_connector->_googleClient);
$params = array('mine' => true,'maxResults'=>25,'order'=>'alphabetical');
$part = 'snippet,contentDetails';
$response = $this->_youtube->subscriptions->listSubscriptions(
$part,
$params
);
foreach ($response['items'] as $item) {
$this->_mysubscriptions[] = array(
'channelId'=>$item['snippet']['resourceId']['channelId'],
'title'=>$item['snippet']['title'],
'description'=>$item['snippet']['description'],
'thumb_default'=>$item['snippet']['thumbnails']['default']['url'],
'thumb_medium'=>$item['snippet']['thumbnails']['medium']['url'],
'thumb_high'=>$item['snippet']['thumbnails']['high']['url'],
'subscribedOn'=>$this->cleanDate($item['snippet']['publishedAt']),
'totalVideos'=>$item['contentDetails']['totalItemCount'],
'newVideos'=>$item['contentDetails']['newItemCount']);
}
This is how the object returned looks like (just removed few IDs from the response) from the google API explorer, while when I run it through my code I get the same data but the newItemCount is zero.
{
"kind": "youtube#subscription",
"snippet": {
"publishedAt": "2016-09-14T12:48:00.000Z",
"title": "Muselk",
"description": "\"Memes win games\" - Youtube.com/mrmuselk",
"resourceId": {
"kind": "youtube#channel",
"channelId": "UCd534c_ehOvrLVL2v7Nl61w"
},
"thumbnails": {
"default": {
"url": "https://yt3.ggpht.com/-iWlz7dePNz0/AAAAAAAAAAI/AAAAAAAAAAA/smtPKh-RLTU/s88-c-k-no-mo-rj-c0xffffff/photo.jpg"
},
"medium": {
"url": "https://yt3.ggpht.com/-iWlz7dePNz0/AAAAAAAAAAI/AAAAAAAAAAA/smtPKh-RLTU/s240-c-k-no-mo-rj-c0xffffff/photo.jpg"
},
"high": {
"url": "https://yt3.ggpht.com/-iWlz7dePNz0/AAAAAAAAAAI/AAAAAAAAAAA/smtPKh-RLTU/s240-c-k-no-mo-rj-c0xffffff/photo.jpg"
}
}
},
"contentDetails": {
"totalItemCount": 792,
"newItemCount": 4,
"activityType": "all"
}
I've looked through the revision history but can't find any reference of modifications made to this specific property of the contentDetails object
There is a bug filed with google on this property but it refers to a different behaviour.
Wondering if this happens to other as well, or if somebody can give some hints on how this works or don't.