Posted by dellus on Oct 17, 2017; 6:36pm
URL: https://forum.librecad.org/Dimension-guides-different-length-tp5715382p5715384.html

The extension lines (guide lines) do not react to trim or other modifying commands.
You could additionally activate "snap to entity" and when you want a short extension line on the symmetry axis then click on that somewhere at a place which gives a short extension line, you don't have to hit an endpoint or intersection.