Ember 2, Strange behaviour with isPending, isSettled, isFulfilled when using included relationships in API response

I need to understand once for all why property like

isSettled isPending isFulfilled

are different if I'm including or not the data in my API respone.

I'm asking here this: http://ift.tt/2n6Za4d which leads me to this strange behaviour:

If I include in my API responde the data (ex: model.posts) these properties are immediately set to true (and .isPending to false) also if Chrome is still loading the real data (also for the first time!).

And this is a problem because I don't know if the posts[] are empty or not and I don't know what I can spy because something like that doesn't work:

  My posts.

  
    <div>Loading...</div>
  
    <div>Nothing to show.</div>
  

It's always "Nothing to show." until Chrome loads. Because .isPending is immediately false.

Also if I use the length attributes:

because the starting posts[] array and the empty one is always to length == 0.

If I loads posts differently, async, not sideloaded (but with hundreds HTTP requests, which I don't want) it works. Ember recognize an isPending...

Why this strange behaviour?