got any other fullscreen game you can try in 1920x1080 mode? That should tell if you if its something in windows, or in blockland.
IMO the problem is with 2 things:
1) Its a TV, not a monitor
2) your running via HDMI and not a standard VGA Cable.
I can easily run GTA 4 on 1920 x 1080 aswell as:
Sims 3
Roller Coaster Tycoon 3
Biohazard 5
Spore
Emulators (PJ64 and Dolphin though they dont fully use the 1920 x 1080)
They work perfectly fine with both screens plugged in and display correctly on the TV. So my conclusion comes with either Blockland or Blockland hates me :P
Here, I will post pic of GTA for that matter, give me a sec