Clicking on port creates stray edge

[sswatson]

Clicking on a port sometimes creates an edge to the top left of the canvas (the point (0, 0), I think).

You can observe this behavior in the demo: http://projectstorm.cloud/react-diagrams/?path=/story/customization--custom-diamond-node. Just click on one of the corner ports on the custom diamond node.

Is there a way to prevent this behavior?