This is printed in the manual under "What's changed in 5.09"
Item 5 ) NEW
- Dual Display - We made a change to make this more reliable. If your Video Card shows your primary monitor as number 2 and the TV as 1, prior versions would not go full screen on the correct monitor. It would jump back to your Desktop. You would then have to drag the screen to the Tv, and stretch it out to fill the screen. You now can double click and we will match the Primary screen so that we always find the intended singers monitor.
So if yours is not working maybe something not right with that change.
I have ATI Radion graphics card and mine works fine with the HDMI connected.
It may be a Windows 8 thing, as I don't have Windows 8 I can only guess.
There are other controls on mine for switching monitors under the advanced section, to get to them:
Again right click desktop, select screen resolution then select Advanced, then the ATI control centre tab then another big button in the middle for Ati catalyst control centre, in the top left corner is a graphics dropdown, select desktop displays from there, this shows a similar thing as windows, 2 screens side by side but you can right click on No1 screen and select swap.
So if the previous settings didn't work might be worth trying that.