Could be the app specific itself.
Not all apps are 'castable' or Airplay-able itself.
I know this came up with Shomi early on.. you could watch on the phone itself.. but you could not cast or airplay the content to an airplay device like an apple TV.
This was later changed with the Shomi app.. works now.
(weither this part is true or not.. I have read some things that this was designed around licensing.. as when you pay for X service, you pay for YOU to watch it. With something like airplay.. you could then cast it anywhere.. in an environment where there are 1000's of people who have not paid for it..
Again, weither this is right no not.. is beyond me)
Rogers 9865, LG 47LV5400 LED TV, Onkyo HT-R690.