Posted by ravas on Apr 12, 2016; 10:29pm
URL: https://forum.librecad.org/Bugg-on-Offset-tool-in-Modify-tp5713460p5713461.html

Do all of your selecting first, then activate a modify tool.

The rectangle is now a polyline, instead of a collection of line segments.
Try using 'Create Equidistant Polylines' instead of offset.