Issue with the plotting of two vectors

I don't know how Mathcad interprets your data format and why it draws all points but only one line and also I don't know why its drawing the lines you expect when you slightly change the data. Maybe Mathcad gets confused because even in a waterfall plot, where on the ordinate you usually have a matrix with more than one column, on the abscissa there still is expected a one column vector.

To plot a polygon you usually would provide a 9x1 vector with x-coordinates for the abscissa and a 9x1 vector with y-coordinates for the ordinate. If you want to suspend connecting the points you would insert a NaN in those vectors.

As a quick hack you can plot the transposed of your matrices. But this will only work if each value in the first row is the very same as the value one column earlier in the second row.

ADDENDUM: I just noticed that probably you ran into a bug in Mathcad!

If we plot a series of not connected line segments (separated by NaN's) Mathcad refuses to plot a segment if the start point of it equals the endpoint of the last segment!!

So if it can happen that you don't have a polygon with all points connected, I would write a small program which post-processes the output of your Sections and Load program and creates the correct data structure considering that bug (= insert a NaN only if necessary).