Dear Xara...

Create a Red triangle with the QuickShape tool with a Rotation of 90°
Convert it to Editable Shapes and delete the edge nodes, leaving a simple equilateral triangle.
Any similar construction will do so that there is a node with an angle of -90°.

Change the -90° to 90°. The node and connected downward line should invert.
Nothing happens.

All works for any other angle - try -91° to 91°.

Acorn