Posted by dxli on Jun 05, 2013; 1:36pm
URL: https://forum.librecad.org/Bug-rs-actiondrawellipsecenter3point-tp5708194p5708223.html

Just make sure you don't miss this commit:

https://github.com/LibreCAD/LibreCAD/commit/f2b089680b7ccf9f849a894a4feaf94b0800c81f

-    if( (l1.isValid()==false && l2.isValid()) == false ) {
+    if( (l1.isValid()==false || l2.isValid()) == false ) {

The logic is clear: do not do intersection if any quadratic is invalid.