Glue points lost on sphere

In Draw I want to connect connectors to the centre of spheres.

I have added a glue point to the centre of the sphere and successfully connect a line to the centre of a sphere.

However, when I close and reopen the file the glue points have been lost and the lines are connected to the edge of the sphere and not the centre?

How do I get the glue points to, err, glue?

What are your LO version and OS+version?