Take a spline and enable Closed Loop.
The segment of the spline which gets generated between the last and the first point has an incorrect tangent. It does take the tangent correctly from the last point, but not the tangent from the first point.
Selected point is the last point, the incorrect tangent is on the bottom right.
Moving the points closer reveals that that incorrect tangent is not 0, but in the direction of the previous point. Also, the length/strength of it does not seem to change.
This is in version 4.7.6