Thank you very much for your help in this case so far!
I have received an explanation from the development: unfortunately, this is a known consequence of the current implementation on how the elements are drawn in the PDF export.
In the output (PDF, print) the drawing border is not used as a clip polygon, the lines are cut shorter instead. But this causes that the line endings are visible at the end. So the line ends at the border of the drawing, but the round line ending goes out of the border.
To change this behavior, it will be a very big task. The whole area has many design questions as well, e.g. if we clip with the drawing contour, the lines that are exactly at the edge of the drawing would be visible only with half of their thickness.
Due to this, other than what Barry mentioned, we don't have any other solution for this.
I'm very sorry for the inconvenience! Please let me know if you have any further questions!
Technical Support Engineer