Registered panel not reopened on Rhino restart

In Rhino 7, if one of my panels was open when Rhino was closed, it would be reloaded when Rhino was started again.

In contrast, in Rhino 8 I see 'Right Container' Container is empty instead of the UI when Rhino is restarted. When the user then manually closes and opens the panel, the UI appears as expected.

The plug-in is loaded at startup.

Do I need to do something different in Rhino 8? Or is this a bug?

I had not yet used the PanelType.System override in RegisterPanel, but that makes no difference.
(Also, I’m testing this on the Rhino 8 beta version)

I have tracked this down to specifics in my codebase that I need to adjust; this is not a problem in Rhino.