In a typical scenario. You must remember that Dynamo is not typical. It is working in a very interesting way within Revit while inside of the Idling event. Even if what my GIF demonstrated “was out of the norm”, it is most definitely something that can happen to any user. Which makes it worth considering as a package developer.
To simply dismiss that as “expected behavior” is irresponsible in my very honest opinion.
But, I thought I would share my experiences with those processes since this community is for sharing our discoveries and our struggles. I look forward to seeing what you find with your continued exploration. 
Also, that link you included is mimicking a double click on a Revit file or on the Revit.exe itself. This is not related to this discussion on using the Revit API’s background open methods within a valid Revit application context. 
The correct way of doing this in non-Dynamo applications is to OpenAndActivateDocumentFile.