The only conditions I can see this happening is if some piece of desolate, windswept desert laid on the border which would provide no use. Some piece of land which would be more trouble to secure than holding it was worth.
Has any two countries ever squabbled, trying to pass off responsibility for some piece of territory on the other?
Sudan and Egypt both consider Bir Tawil to be the territory of the other. This is because they both consider it to be a trading piece of a far more valuable disputed territory: the Halai'b Triangle. I know that I'd like it a top-level comment to have more detail, but all I have is wikipedia.