I used a camera which follows a nurbs path and 'damped track' to an empty.
At some moments on the path the camera rotates around its Z axis in a way that seems not what we could expect (I think ?), especially considering the associated tooltip which says : "points toward a target performing the smallest rotation necessary".
You can see a gif of it here : http://blender.stackexchange.com/questions/58812/damped-track-is-this-behavior-expected.
The blend file :