There is not much difference between _ViewCaptureToFile and _ViewCaptureToClipboard. The exact same code path is followed up until either putting the image in clipboard or saving to file. It is the step prior to this that the managing of the render result fails, it is somewhere in Rhino core code, and https://mcneel.myjetbrains.com/youtrack/issue/RH-45147 is indeed the YT item for this, assigned to @andy.
With either capture command using the steps outlined above you should be able to find the RC_modal_renderer.png as mentioned. Or otherwise use the rhino-render-next test package through the beta package manager that can be started with _TestPackageManager.