In the last moments of The Time of the Doctor, when the young man enters the tower, the Doctor says that "he got a plan", then tells Clara that he got no plan.

But the city has a Truth Field created by Gallifrey, comming through the crack on the wall.

So, how could the Doctor lie in this moment?

In the last moments of The Time of the Doctor, when the young man enters the tower, the Doctor says that he has a plan, and then tells Clara that actually, he has no plan.

But the city has a truth field created by Gallifrey coming through the crack in the wall.

So, how could the Doctor lie at this moment?