Line corners plotted to a .PDF file are not squared.
The current setting is for linejoin=0(mitered).
However, line corners meeting at an angle do not come out nicely mitered.
Instead, each line is squared off individually.
The two lines were actually two individual lines, not a line string.
Therefore, linecap needs to be used rather than linejoin.
The Max Miter Angle in the .pltcfg Advanced section was set at 90 degrees.
Reset this to 59 degrees and the mitered corners come out as before.