I have just finished an intense 2D drafting project in Rhino v 6 sr13. It seems there is a breakdown in the dimension tools in that when I click Vertical Dimension button - point 1 - point 2. If the horizontal distance between points 1 & 2 is greater than the vertical distance, I get a horizontal dimension - NOT a vertical dimension. The same case plays out for Horizontal Dimension button as well. The Linear Dimension tool performs as expected but it is helpful to constrain to the preferred axis.