Okay, an update re this behaviour. I've worked out that Freeview on Demand has some sort off issue with certain other inputs on the TV. It works fine if switching from normal aerial TV channels to FOD but it absolutely hates switching from my Vodafone TV cable box (T-Box) to FOD. If I am on the T-box and then switch to FOD it loads but freezes and the T-Box sound continues to play. Its very much as if the Samsung software is not able to adequately switch over.
Seems logical. Freeview states that a UHF (or Sat Dish) must be connected for FOD to work. Therefore it seems logical to me that the TV must be switched to a live channel to use FOD so that FOD can achieve the necessary interaction with the broadcast EPG. If any other input is selected then the broadcast EPG will be absent. Maybe someone from Freeview could comment?
Its already all connected, it seems odd that the FV app is so picky as to require a specific precursor source given that FV On demand itself is just another source.
Once you figure out what it wants its no biggie but it makes little logical sense as a user.