From what I can guess at, what's happening is that the camera doesn't think in just 360 degrees, it also remembers how many times you've spun the camera while making the other keyframes. This often results in it having to make a 1080 degree spin or such between the 2nd last keyframe & the end of the block, which would also make it act weird from the 3rd last keyframe when it starts building momentum for the last bit.
For an easier fix, select the last keyframe, and hold ctrl while clicking the 2nd last keyframe. This will copy all of the numbers from the 2nd last keyframe to the last keyframe without having to type it inn, and you can re-position it from there.
Alternatively, all you have to fix / copy is the Pitch, Yaw & Roll numbers.
Which will copy the direction the camera faces without changing position or zoom.
