Posted by UserError on Feb 12, 2020; 8:17pm
URL: https://forum.librecad.org/Suddenly-lines-go-to-infinity-tp5718396p5718400.html

Many thanks. I hadn't involved myself with construction lines so I must have somehow inadvertantly toggled it on!
My version is the one in the Linux Mint repository.  I know they often lag behind but I tend to play it safe as I've had no end of PPA problems when I've added them.
Cheers.