In the below image, I right clicked on the diagram where the red circle indicates, but the context menu appeared up and to the left of my mouse position.
The same thing occurs on nodes.
I’m running GoJS v1.8.27; in Chrome, the context menus appear in the expected position.
I’m not sure if something could affect the coordinates that the mouseEvent returns? Is the mouseEvent coordinate here relative to the edge of the GoJS diagram or the browser window? The difference from where I click to the top of the context menu seems consistent with the space between the top of the diagram and the top of the IE window.