Lithium Community 18.7 Release Notes

luk I just tried this query

select select id, author.login, user_context.is_subscribed from messages where id = '915'

and got this response

{
  "status" : "success",
  "message" : "",
  "http_code" : 200,
  "data" : {
    "type" : "messages",
    "list_item_type" : "message",
    "size" : 1,
    "items" : [ {
      "type" : "message",
      "id" : "915",
      "author" : {
        "type" : "user",
        "login" : "ProductPerson"
      },
      "user_context" : {
        "type" : "user_context",
        "is_subscribed" : true
      }
    } ]
  },
  "metadata" : { }
}

I also was able to get "is_subscribed" : true when I only used user_context in the select statement (without the .is_subscribed field specified) and without filtering for a specific message as well. I was able to see messages where is_subscribed = true.  

I'm not sure why this isn't working for you.