Yeah i had the same issue on the squad selection screen.
Seems that for some reason the default location for the squad list is anchored to the far left, yet on this screen it has black borders at both sides rendering most of the left and right final 1/3 unviewable :(
Had to resort to playing on 1 screen which is a mighty shame.
But the issue is only on the screen
before the actual gameplay, why play in 1 screen? Im still in Triple and the few times I want to swap the Sniper for the Jetpack guy before the mission I Exit to Menu, change res, Campaign, swap guys, Exit To Menu, change res and back in. Takes about 30sec as the loading is so fast.
Playing the 3D action (ie the game) is great in Triplehead!