Clicking a reference to a node that is rendered as an edge in a graphical editor, doesn't select this edge in the diagram of the graphical editor

If I make a reference to a node that has a diagram.box as editor, then I can click this reference and the box will be selected in the editor.
If I do the same with a reference to a node that has a diagram.edge as editor, then this edge doesn't get selected.

Issue moved from https://github.com/mbeddr/mbeddr.core/issues/1445.

Start by reproducing the behavior in the graphical editor with references to nodes using diagram.box and diagram.edge editors. Compare selection behavior after clicking each reference; done means clicking the edge reference selects the corresponding edge in the diagram.

Written by the indexing model from the issue text.