page-id/notifications returns an empty array - facebook

Question

I'm writing a desktop application using Facebook SDK .NET. This app must do somethink for every post, comment or message sent to a Facebook page. I'm using the page-id/notifications API command:
page-id/notifications?fields=id,title,unread,application,from,message,object&limit=250
This command returns correct unseen count in summary section but data array is empty:
{
"data": [
],
"summary": {
"unseen_count": 2,
"updated_time": "2016-02-05T14:53:10+0000"
}
}
If someone write a new wall post on the page or send a private message to the page, unseen_count is updated but data array is always empty. If someoune write a comment to an exisiting wall post unseen_count is updates and data array is populated with a comment notification (only this type of notification are added to data array):
{
"data": [
{
"id": "notif_XXXXXXXXXXXXXXX_XXXXXXXXXXXXXXXX",
"title": "yyyyy yyyyyyy commented on his post.",
"unread": 1,
"application": {
"link": "https://www.facebook.com/games/?app_id=xxxxxxxxxxx",
"name": "Feed Comments",
"id": "1967xxxxxxx"
},
"from": {
"name": "Mxxxx Sxxxxxx",
"id": "1020xxxxxxxxxxxxx"
},
"object": {
"created_time": "2016-02-05T14:52:32+0000",
"message": "ABCDEFGHILMNOPQRSTUVZ",
"id": "36xxxxxxxxxxxx0_546xxxxxxxxxxx0"
},
"to": {
"name": "Ixxxxxxx",
"id": "36xxxxxxxxxxxxx"
}
}
],
"paging": {
"previous": "xxxxxxxxxxxxxxxxxxxxxxxxxx",
"next": "xxxxxxxxxxxxxxxxxxxx
},
"summary": {
"unseen_count": 3,
"updated_time": "2016-02-05T14:55:23+0000"
}
}
Is it an API bug or there is something wrong in my API request?
I CANNOT use real time notification.
Thanks
Marco