I have the exact same issue except I am using the RTM release of 8.1. On my main monitor the mouse cursor is normal sized @ 1080p, On my LG LCD TV @ 1080p the mouse cursor is quadruple the size. All resolutions are at native.
I have also notice when I drag vlc player onto the TV it also appears to have increased in size (navigation bar, menus, everything). One more thing I have noticed is when I drag my browser over the page zoom doubles automatically (if I drop the zoom to 100% then drag it back to my main monitor it drops to 50%). Due to using windows 8.1 I am using the beta release 326.80 for my 780.
PS if I drop my resolution on the tv to 1680 x 1050 everything works as normal