When I go to the terrain thing to add mountains and ditches etc. I find that when I click while holding control, I do not create different terrain, instead, the camera just moves as if I were not holding down control at all
On the mountain looking button menu (forgive me, I do not know the proper names), where it says "Heightmap", I clicked on it, and it appears highlighted, but that doesn't make one bit of difference. Also, I have tried it on locked and unlocked, doesn't matter.
By the way, whenever I get frustrated dealing with that, and try something else on the same file, I find I have trouble with the z axis and the move texture button (the one to the right of the mountain button)